Methods for hydrocarbon recovery

ABSTRACT

Provided herein are liquid polymer (LP) compositions comprising a synthetic (co)polymer (e.g., an acrylamide (co)polymer), as well as methods for preparing inverted polymer solutions by inverting these LP compositions in an aqueous fluid. The resulting inverted polymer solutions can have a concentration of a synthetic (co)polymer (e.g., an acrylamide (co)polymer) of from 50 to 15,000 ppm, and a filter ratio of 1.5 or less at 15 psi using a 1.2 μm filter. Also provided are methods of using these inverted polymer solutions in oil and gas operations, including enhanced oil recovery.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of U.S. Provisional Application No.62/264,776, filed Dec. 8, 2015, which is hereby incorporated herein byreference in its entirety.

BACKGROUND

Water-soluble polymers such as polyacrylamide and copolymers ofacrylamide with other monomers are known to exhibit superior thickeningproperties when said polymers are dissolved in aqueous media.Particularly well-known for this purpose are the anionic carboxamidepolymers such as acrylamide/acrylic acid copolymers, including thoseprepared by hydrolysis of polyacrylamide. Such polymers can be used asfluid mobility control agents in enhanced oil recovery (EOR) processes.

In the past, these polymers were made available commercially as powdersor finely divided solids which were subsequently dissolved in an aqueousmedium at their time of use. Because such dissolution steps aresometimes time consuming and often require rather expensive mixingequipment, such polymers are sometimes provided in water-in-oilemulsions wherein the polymer is dissolved in the dispersed aqueousphase. The water-in-oil emulsions can then be inverted to formoil-in-water emulsions at their time of use. Unfortunately for manyapplications, existing water-in-oil emulsions do not invert as readilyas desired. Furthermore, the resulting inverted emulsions are oftenunable to pass through porous structures. This significantly limitstheir utility as, for example, fluid mobility control agents in EORapplications. In addition, existing water-in-oil emulsions often cannotbe efficiently inverted using an aqueous medium containing dissolvedsalts, as is often the case for enhanced oil recovery practices.

SUMMARY

Provided herein are methods for preparing inverted polymer solutions.Methods for preparing inverted polymer solutions can comprise invertingan LP composition comprising one or more synthetic (co)polymers (e.g.,one or more acrylamide (co)polymers) dispersed or emulsified in one ormore hydrophobic liquids to provide an inverted polymer solution havinga concentration of one or more synthetic (co)polymers (e.g., one or moreacrylamide (co)polymers) of from 50 to 15,000 ppm.

For example, in some embodiments, methods for preparing inverted polymersolutions can comprise providing a liquid polymer (LP) compositioncomprising one or more hydrophobic liquids having a boiling point atleast 100° C.; at least 39% (e.g., greater than or equal to 39%) byweight of one or more synthetic (co)polymers (e.g., one or moreacrylamide (co)polymers); one or more emulsifier surfactants; and one ormore inverting surfactants; and inverting the LP composition in anaqueous fluid to provide an inverted polymer solution having aconcentration of synthetic (co)polymer of from 50 to 15,000 ppm (e.g.,from 500 to 5000 ppm). In other embodiments, methods for preparinginverted polymer solutions can comprise providing a liquid polymer (LP)composition in the form of an inverse emulsion comprising one or morehydrophobic liquids having a boiling point at least 100° C.; up to 35%by weight of one or more synthetic (co)polymers (e.g., one or moreacrylamide (co)polymers); one or more emulsifier surfactants; and one ormore inverting surfactants; and inverting the LP composition in anaqueous fluid to provide an inverted polymer solution having aconcentration of synthetic (co)polymer of from 50 to 15,000 ppm (e.g.,from 500 to 5000 ppm). In other embodiments, methods for preparinginverted polymer solutions can comprise providing a liquid polymer (LP)composition in the form of an inverse emulsion comprising one or morehydrophobic liquids having a boiling point at least 100° C.; up to 38%by weight of one or more synthetic (co)polymers (e.g., one or moreacrylamide (co)polymers); one or more emulsifier surfactants; and one ormore inverting surfactants; and inverting the LP composition in anaqueous fluid to provide an inverted polymer solution having aconcentration of synthetic (co)polymer of from 50 to 15,000 ppm (e.g.,from 500 to 5000 ppm). The inverted polymer solutions can exhibit afilter ratio of 1.5 or less (e.g., a filter ratio of 1.2, a filter ratioof 1.2 or less, and/or a filter ratio of from 1.1 to 1.3) at 15 psiusing a 1.2 μm filter.

In some embodiments, inversion of the LP composition comprises a singlestep. For example, in some cases, the inversion of the LP compositioncan comprise diluting the LP composition in the aqueous fluid in anin-line mixer to provide the inverted polymer solution. The in-linemixer can be a static mixer or a dynamic mixer (e.g., an electricalsubmersible pump, a hydraulic submersible pump, or a progressive cavitypump). In certain embodiments, the in-line mixer is positioned on thesurface, subsurface, subsea, or downhole.

In other embodiments, inversion of the LP composition can comprises twoor more steps. For example, in some cases, the inversion of the LPcomposition can comprise as a first step, inverting the LP compositionin the aqueous fluid in a first in-line mixer to provide a concentratedpolymer composition having a concentration of synthetic (co)polymer(e.g., one or more acrylamide (co)polymers) of up to 15,000 ppm; and asa second step, diluting the concentrated polymer composition in theaqueous fluid in a second in-line mixer to provide the inverted polymersolution. The first in-line mixer and the second in-line mixer can eachindividually be a static mixer or a dynamic mixer (e.g., an electricalsubmersible pump, a hydraulic submersible pump, or a progressive cavitypump). In certain embodiments, the second in-line mixer is positioned onthe surface, subsurface, subsea, or downhole.

Also provided herein are method for hydrocarbon recovery. The methodsfor hydrocarbon recovery can comprise providing a subsurface reservoircontaining hydrocarbons there within; providing a wellbore in fluidcommunication with the subsurface reservoir; preparing an invertedpolymer solution according to the methods described herein; andinjecting the inverted polymer solution through the wellbore into thesubsurface reservoir. The wellbore in the second step can be aninjection wellbore associated with an injection well, and the method canfurther comprise providing a production well spaced apart from theinjection well a predetermined distance and having a production wellborein fluid communication with the subsurface reservoir. In theseembodiments, injection of the inverted polymer solution can increase theflow of hydrocarbons to the production wellbore. In some embodiments,the wellbore in the second step can be a wellbore for hydraulicfracturing that is in fluid communication with the subsurface reservoir.

DESCRIPTION OF DRAWINGS

FIG. 1 is a process flow diagram illustrating a single step process forpreparing an inverted polymer solution.

FIG. 2 is a process flow diagram illustrating a two-step process forpreparing an inverted polymer solution.

FIGS. 3A and 3B are process flow diagrams illustrating a plurality ofprocesses for preparing inverted polymer solutions.

FIG. 4 illustrates an in-line injection system that can be used inconjunction with the compositions and methods described herein.

FIG. 5 illustrates an alternative in-line injection system that can beused in conjunction with the compositions and methods described herein.

FIG. 6 illustrates an alternative in-line injection system that can beused in conjunction with the compositions and methods described herein.

FIG. 7 illustrates an alternative in-line injection system that can beused in conjunction with the compositions and methods described herein.

FIG. 8 illustrates an alternative in-line injection system that can beused in conjunction with the compositions and methods described herein.

FIG. 9 illustrates an alternative in-line injection system that can beused in conjunction with the compositions and methods described herein.

FIG. 10 is a plot of the pressure drop and relative permeability uponinjection of an inverted polymer solution in a sandstone core. Thesteady pressure drop and steady relative permeability observed uponinjection of the inverted polymer solution are consistent with noplugging of the sandstone core.

FIG. 11 is a plot of the filtration ratio test performed using a 1.2micron filter for an inverted polymer solution. The inverted polymersolution (2000 ppm polymer) passes through 1.2 micron filter with afilter ratio of less than 1.2, which shows improved filterability of theinverted polymer solution.

FIG. 12 is a viscosity plot in the wide range of shear rate for aninverted polymer solution (2000 ppm polymer in synthetic brine, measuredat 31° C.). The viscosity of the inverted polymer solution shows atypical shear-thinning behavior in the wide range of shear rate. Theviscosity is measured as 24 cP at 10 s−1 and 31° C.

FIG. 13 is a viscosity plot in the wide range of shear rate for neat LPcomposition activity of the neat LP composition test here is 50% and theviscosity of LP is measured at 180 cP at 10 s⁻¹ and 25° C. Low viscositywith high activity makes the LP composition easy to handle in the field.

FIG. 14 is an oil recovery and pressure drop plot for an inverted LPsolution (2000 ppm polymer) in unconsolidated-sand pack. Oil recoveryincreases as the inverted LP is injected while pressure drop for LPinjection shows steady-state and low at the end of the experiment. Thesteady-state low pressure drop from LP at the end of the experimentindicates improved behavior as the LP solutions do not plug the coreduring oil recovery.

FIG. 15 is a plot showing the LP viscosity as a function ofconcentration at a temperature of 31° C. and shear rate of 10 sec⁻¹.

FIG. 16 is a plot of LP shear viscosities as a function of shear rate ata temperature of 31° C.

FIGS. 17A and 17B are plots of filtration ratio tests performed using a5 micron filter (FIG. 17A) and 1.2 micron filter (FIG. 17B) for invertedpolymer solutions M1-M6. The inverted polymer solution (2000 ppmpolymer) passes through 1.2 micron filter with a filter ratio of lessthan 1.5, which shows improved filterability of the inverted polymersolution.

FIG. 18 is a plot of the pressure drop upon injection of an invertedpolymer solution (2000 ppm) in a sandstone core (1.2 D) with a pressuretab attached at 2″ from the inlet to monitor face plugging. The steadypressure drop observed upon injection of the inverted polymer solutionin both whole and 1^(st) section in the core are consistent with nosignificant plugging of the sandstone core. The inverted polymer wasinjected up to 45 PV followed by post-water flood. The pressure dropduring the post-water flood also showed that injection of the invertedpolymer solution did not plug the core.

FIG. 19A is a plot of the normalized permeability reduction of aninverted conventional liquid polymer LP #1 (2000 ppm) in a sandstonewith a pressure tap (3″) showing face plugging at the inlet. FIG. 19B isa plot of the normalized permeability reduction of the inverted LPcomposition (2000 ppm) in a sandstone with a pressure tap (2″) showingno significant plugging above 250 PV of injection at inlet.

FIG. 20 is a plot of the Permeability Reduction Factor (R_(k)) andNormalized Skin Factor, s/ln(r_(s)/r_(w)) as a function of thefiltration ratio at 1.2 μm (FR_(1.2)). R_(k) and skin factor werecalculated at 25 PV of injection into sandstone core.

FIG. 21 is a bar graph illustrating the viscosity yield achieving usingmulti-step (two) mixing configurations and single step mixingconfigurations with and without a dynamic mixer.

FIG. 22A is a plot of the viscosity yield as a function of the pressuredrop across the static mixer(s).

FIG. 22B is a plot of the filtration ration as a function of thepressure drop across the static mixer(s).

DETAILED DESCRIPTION

Provided herein are liquid polymer (LP) compositions comprising asynthetic polymer, such as an acrylamide (co)polymer, as well as methodsfor preparing inverted polymer solutions by inverting these LPcompositions in an aqueous fluid. Also provided are methods of usingthese inverted polymer solutions in oil and gas operations, includingenhanced oil recovery (EOR).

The term “enhanced oil recovery” refers to techniques for increasing theamount of unrefined petroleum (e.g., crude oil) that may be extractedfrom an oil reservoir (e.g., an oil field). Using EOR, 40-60% of thereservoir's original oil can typically be extracted compared with only20-40% using primary and secondary recovery (e.g., by water injection ornatural gas injection). Enhanced oil recovery may also be referred to asimproved oil recovery or tertiary oil recovery (as opposed to primaryand secondary oil recovery). Examples of EOR operations include, forexample, miscible gas injection (which includes, for example, carbondioxide flooding), chemical injection (sometimes referred to as chemicalenhanced oil recovery (CEOR), and which includes, for example, polymerflooding, alkaline flooding, surfactant flooding, conformance controloperations, as well as combinations thereof such as alkaline-polymerflooding or alkaline-surfactant-polymer flooding), microbial injection,and thermal recovery (which includes, for example, cyclic steam, steamflooding, and fire flooding). In some embodiments, the EOR operation caninclude a polymer (P) flooding operation, an alkaline-polymer (AP)flooding operation, a surfactant-polymer (SP) flooding operation, analkaline-surfactant-polymer (ASP) flooding operation, a conformancecontrol operation, or any combination thereof. The terms “operation” and“application” may be used interchangeability herein, as in EORoperations or EOR applications.

For purposes of this disclosure, including the claims, the filter ratio(FR) can be determined using a 1.2 micron filter at 15 psi (plus orminus 10% of 15 psi) at ambient temperature (e.g., 25° C.). The 1.2micron filter can have a diameter of 47 mm or 90 mm, and the filterratio can be calculated as the ratio of the time for 180 to 200 ml ofthe inverted polymer solution to filter divided by the time for 60 to 80ml of the inverted polymer solution to filter.

${FR} = \frac{{\;^{t}200\mspace{14mu}{ml}} - {{\,{\,^{t}180}}\mspace{14mu}{ml}}}{{\;^{t}80\mspace{14mu}{ml}} - {{\,^{t}60}\mspace{14mu}{ml}}}$For purposes of this disclosure, including the claims, the invertedpolymer solution is required to exhibit a FR of 1.5 or less.

The inversion of conventional inverse emulsion polymers can bechallenging. For use in many applications, rapid and complete inversionof the inverse emulsion polymer composition is required. For example,for many applications, rapid and continuous inversion and dissolution(e.g., complete inversion and dissolution in five minutes or less) isrequired. For certain applications, including many oil and gasapplications, it can be desirable to completely invert and dissolve theemulsion or LP to a final concentration of from 500 to 5000 ppm in anin-line system in a short period of time (e.g., less than five minutes).

For certain applications, including many enhanced oil recovery (EOR)applications, it can be desirable that the inverted composition flowsthrough a hydrocarbon-bearing formation without plugging the formation.Plugging the formation can slow or inhibit oil production. This is anespecially large concern in the case of hydrocarbon-bearing formationsthat have a relatively low permeability prior to tertiary oil recovery.

One test commonly used to determine performance of the emulsion or LP insuch conditions involves measuring the time taken for givenvolumes/concentrations of solution to flow through a filter, commonlycalled a filtration quotient or Filter Ratio (“FR”). For example, U.S.Pat. No. 8,383,560 describes a filter ratio test method which measuresthe time taken by given volumes of a solution containing 1000 ppm ofactive polymer to flow through a filter. The solution is contained in acell pressurized to 2 bars and the filter has a diameter of 47 mm and apore size of 5 microns. The times required to obtain 100 ml (t100 ml),200 ml (t200 ml), and 300 ml (t300 ml) of filtrate were measured. Thesevalues were used to calculate the FR, expressed by the formula below:

${FR} = \frac{{\;^{t}300\mspace{14mu}{ml}} - {{\,^{t}200}\mspace{14mu}{ml}}}{{\;^{t}200\mspace{14mu}{ml}} - {{\,^{t}100}\mspace{14mu}{ml}}}$

The FR generally represents the capacity of the polymer solution to plugthe filter for two equivalent consecutive volumes. Generally, a lower FRindicates better performance. U.S. Pat. No. 8,383,560, which isincorporated herein by reference, explains that a desirable FR usingthis method is less than 1.5.

However, polymer compositions that provide desirable results using thistest method, have not necessarily provided acceptable performance in thefield. In particular, many polymers that have an FR (using a 5 micronfilter) lower than 1.5 exhibit poor injectivity—i.e., when injected intoa formation, they tend to plug the formation, slowing or inhibiting oilproduction. A modified filter ratio test method using a smaller poresize (i.e., the same filter ratio test method except that the filterabove is replaced with a filter having a diameter of 47 mm and a poresize of 1.2 microns) and lower pressure (15 psi) provides a betterscreening method. Inverted polymer solutions prepared by the methodsdescribed herein can provide a FR using the 1.2 micron filter of 1.5 orless. In field testing, these compositions can exhibit improvedinjectivity over commercially-available polymer compositions—includingother polymer compositions having an FR (using a 5 micron filter) ofless than 1.5. As such, the inverted compositions described herein aresuitable for use in a variety of oil and gas applications, includingEOR.

LP Compositions

LP compositions can comprise one or more synthetic (co)polymers (e.g.,one or more acrylamide (co)polymers) dispersed or emulsified in one ormore hydrophobic liquids. In some embodiments, the LP compositions canfurther comprise one or more emulsifying surfactants and one or moreinverting surfactants. In some embodiments, the LP compositions canfurther comprise a small amount of water. For example, the LPcompositions can further comprise less than 10% by weight (e.g., lessthan 5% by weight, less than 4% by weight, less than 3% by weight, lessthan 2.5% by weight, less than 2% by weight, or less than 1% by weight)water, based on the total weight of all the components of the LPcomposition. In certain embodiments, the LP compositions can bewater-free or substantially water-free (i.e., the composition caninclude less than 0.5% by weight water, based on the total weight of thecomposition). The LP compositions can optionally include one or moreadditional components which do not substantially diminish the desiredperformance or activity of the composition. It will be understood by aperson having ordinary skill in the art how to appropriately formulatethe LP composition to provide necessary or desired features orproperties.

In some embodiments, the LP composition can comprise one or morehydrophobic liquids having a boiling point at least 100° C.; at least39% by weight of one or more synthetic co-polymers (e.g.,acrylamide-(co)polymers); one or more emulsifier surfactants; and one ormore inverting surfactants.

In some embodiments, the LP composition can comprise one or morehydrophobic liquids having a boiling point at least 100° C.; at least39% by weight of particles of one or more acrylamide-(co)polymers; oneor more emulsifier surfactants; and one or more inverting surfactants.In certain embodiments, when the composition is fully inverted in anaqueous fluid, the composition affords an inverted polymer solutionhaving a filter ratio (FR) (1.2 micron filter) of 1.5 or less. Incertain embodiments, the inverted polymer solution can comprise from 500to 5000 ppm (e.g., from 500 to 3000 ppm) active polymer, and have aviscosity of at least 20 cP at 30° C.

In some embodiments, the LP compositions can comprise less than 10% byweight (e.g., less than 7% by weight, less than 5% by weight, less than4% by weight, less than 3% by weight, less than 2.5% by weight, lessthan 2% by weight, or less than 1% by weight) water prior to inversion,based on the total weight of all the components of the LP composition.In certain embodiments, the LP composition, prior to inversion,comprises from 1% to 10% water by weight, or from 1% to 5% water byweight, based on the total amount of all components of the composition.

In some embodiments, the solution viscosity (SV) of a 0.1% solution ofthe LP composition can be greater than 3.0 cP, or greater than 5 cP, orgreater than 7 cP. The SV of the LP composition can be selected based,at least in part, on the intended actives concentration of the invertedpolymer solution, to provide desired performance characteristics in theinverted polymer solution. For example, in certain embodiments, wherethe inverted composition is intended to have an actives concentration ofabout 2000 ppm, it is desirable that the SV of a 0.1% solution of the LPcomposition is in the range of from 7.0 to 8.6, because at this level,the inverted solution has desired FR1.2 and viscosity properties. Aliquid polymer composition with a lower or higher SV range may stillprovide desirable results, but may require changing the activesconcentration of the inverted composition to achieve desired FR1.2 andviscosity properties. For example, if the liquid polymer composition hasa lower SV range, it may be desirable to increase the activesconcentration of the inverted composition.

In some embodiments, the LP composition can comprise one or moresynthetic (co)polymers (e.g., one or more acrylamide (co)polymers)dispersed in one or more hydrophobic liquids. In these embodiments, theLP composition can comprise at least 39% polymer by weight (e.g., atleast 40% by weight, at least 45% by weight, at least 50% by weight, atleast 55% by weight, at least 60% by weight, at least 65% by weight, atleast 70% by weight, or at least 75% by weight), based on the totalamount of all components of the composition. In some embodiments, the LPcomposition can comprise 80% by weight or less polymer (e.g., 75% byweight or less, 70% by weight or less, 65% by weight or less, 60% byweight or less, 55% by weight or less, 50% by weight or less, 45% byweight or less, or 40% by weight or less), based on the total amount ofall components of the composition.

The these embodiments, the LP composition can comprise an amount ofpolymer ranging from any of the minimum values described above to any ofthe maximum values described above. For example, in some embodiments,the LP composition can comprise from 39% to 80% by weight polymer (e.g.,from 39% to 60% by weight polymer, or from 39% to 50% by weightpolymer), based on the total weight of the composition.

In some embodiments, the LP composition can comprise one or moresynthetic (co)polymers (e.g., one or more acrylamide (co)polymers)emulsified in one or more hydrophobic liquids. In these embodiments, theLP composition can comprise at least 10% polymer by weight (e.g., atleast 15% by weight, at least 20% by weight, at least 25% by weight, orat least 30% by weight), based on the total amount of all components ofthe composition. In some embodiments, the LP composition can compriseless than 38% by weight polymer (e.g., less than 35% by weight, lessthan 30% by weight, less than 25% by weight, less than 20% by weight, orless than 15% by weight), based on the total amount of all components ofthe composition.

The these embodiments, the LP composition can comprise an amount ofpolymer ranging from any of the minimum values described above to any ofthe maximum values described above. For example, in some embodiments,the LP composition can comprise from 10% to 38% by weight polymer (e.g.,from 10% to 35% by weight polymer, from 15% to 30% by weight polymer,from 15% to 35% by weight polymer, from 15% to 38% by weight polymer,from 20% to 30% by weight polymer, from 20% to 35% by weight polymer, orfrom 20% to 38% by weight polymer), based on the total weight of thecomposition.

Hydrophobic Liquid

In some embodiments, the LP composition can include one or morehydrophobic liquids. In some cases, the one or more hydrophobic liquidscan be organic hydrophobic liquids. In some embodiments, the one or morehydrophobic liquids each have a boiling point at least 100° C. (e.g., atleast 135° C., or at least 180° C.). If the organic liquid has a boilingrange, the term “boiling point” refers to the lower limit of the boilingrange.

In some embodiments, the one or more hydrophobic liquids can bealiphatic hydrocarbons, aromatic hydrocarbons, or mixtures thereof.Examples of hydrophobic liquids include but are not limited towater-immiscible solvents, such as paraffin hydrocarbons, naphthenehydrocarbons, aromatic hydrocarbons, olefins, oils, stabilizingsurfactants, and mixtures thereof. The paraffin hydrocarbons can besaturated, linear, or branched paraffin hydrocarbons. Examples ofsuitable aromatic hydrocarbons include, but are not limited to, tolueneand xylene. In certain embodiments, the hydrophobic liquid can comprisean oil, for example, a vegetable oil, such as soybean oil, rapeseed oil,canola oil, or a combination thereof, and any other oil produced fromthe seed of any of several varieties of the rape plant.

In some embodiments, the amount of the one or more hydrophobic liquidsin the inverse emulsion or LP composition is from 20% to 60%, from 25%to 54%, or from 35% to 54% by weight, based on the total amount of allcomponents of the LP composition.

Synthetic (Co)Polymers

In some embodiments, the LP composition includes one or more synthetic(co)polymers, such as one or more acrylamide containing (co)polymers. Asused herein, the terms “polymer,” “polymers,” “polymeric,” and similarterms are used in their ordinary sense as understood by one skilled inthe art, and thus may be used herein to refer to or describe a largemolecule (or group of such molecules) that contains recurring units.Polymers may be formed in various ways, including by polymerizingmonomers and/or by chemically modifying one or more recurring units of aprecursor polymer. A polymer may be a “homopolymer” comprisingsubstantially identical recurring units formed by, e.g., polymerizing aparticular monomer. A polymer may also be a “copolymer” comprising twoor more different recurring units formed by, e.g., copolymerizing two ormore different monomers, and/or by chemically modifying one or morerecurring units of a precursor polymer. The term “terpolymer” may beused herein to refer to polymers containing three or more differentrecurring units. The term “polymer” as used herein is intended toinclude both the acid form of the polymer as well as its various salts.

In some embodiments, the one or more synthetic (co)polymers can be apolymer useful for enhanced oil recovery applications. The term“enhanced oil recovery” or “EOR” (also known as tertiary oil recovery),refers to a process for hydrocarbon production in which an aqueousinjection fluid comprising at least a water soluble polymer is injectedinto a hydrocarbon bearing formation.

In some embodiments, the one or more synthetic (co)polymers comprisewater-soluble synthetic (co)polymers. Examples of suitable synthetic(co)polymers include acrylic polymers, such as polyacrylic acids,polyacrylic acid esters, partly hydrolyzed acrylic esters, substitutedpolyacrylic acids such as polymethacrylic acid and polymethacrylic acidesters, polyacrylamides, partly hydrolyzed polyacrylamides, andpolyacrylamide derivatives such as acrylamide tertiary butyl sulfonicacid (ATBS); copolymers of unsaturated carboxylic acids, such as acrylicacid or methacrylic acid, with olefins such as ethylene, propylene andbutylene and their oxides; polymers of unsaturated dibasic acids andanhydrides such as maleic anhydride; vinyl polymers, such as polyvinylalcohol (PVA), N-vinylpyrrolidone, and polystyrene sulfonate; andcopolymers thereof, such as copolymers of these polymers with monomerssuch as ethylene, propylene, styrene, methylstyrene, and alkyleneoxides. In some embodiments, the one or more synthetic (co)polymer cancomprise polyacrylic acid (PAA), polyacrylamide (PAM), acrylamidetertiary butyl sulfonic acid (ATBS) (or AMPS,2-acrylamido-2-methylpropane sulfonic acid), N-vinylpyrrolidone (NVP),polyvinyl alcohol (PVA), or a blend or copolymer of any of thesepolymers. Copolymers may be made of any combination above, for example,a combination of NVP and ATBS. In certain examples, the one or moresynthetic (co)polymers can comprise acrylamide tertiary butyl sulfonicacid (ATBS) (or AMPS, 2-acrylamido-2-methylpropane sulfonic acid) or acopolymer thereof.

In some embodiments, the one or more synthetic (co)polymers can compriseacrylamide (co)polymers. In some embodiments, the one or more acrylamide(co)polymers comprise water-soluble acrylamide (co)polymers. In variousembodiments, the acrylamide (co)polymers comprise at least 30% byweight, or at least 50% by weight acrylamide units with respect to thetotal amount of all monomeric units in the (co)polymer.

Optionally, the acrylamide-(co)polymers can comprise, besidesacrylamide, at least one additional co-monomer. In example embodiments,the acrylamide-(co)polymer may comprise less than about 50%, or lessthan about 40%, or less than about 30%, or less than about 20% by weightof the at least one additional co-monomer. In some embodiments, theadditional comonomer can be a water-soluble, ethylenically unsaturated,in particular monoethylenically unsaturated, comonomer. Suitableadditional water-soluble comonomers include comonomers that are misciblewith water in any ratio, but it is sufficient that the monomers dissolvesufficiently in an aqueous phase to copolymerize with acrylamide. Insome cases, the solubility of such additional monomers in water at roomtemperature can be at least 50 g/L (e.g., at least 150 g/L, or at least250 g/L).

Other suitable water-soluble comonomers can comprise one or morehydrophilic groups. The hydrophilic groups can be, for example,functional groups that comprise one or more atoms selected from thegroup of O—, N—, S—, and P-atoms. Examples of such functional groupsinclude carbonyl groups >C—O, ether groups —O—, in particularpolyethylene oxide groups —(CH₂—CH₂—O—)_(n)—, where n is preferably anumber from 1 to 200, hydroxy groups —OH, ester groups —C(O)O—, primary,secondary or tertiary amino groups, ammonium groups, amide groups—C(O)—NH— or acid groups such as carboxyl groups —COOH, sulfonic acidgroups —SO₃H, phosphonic acid groups —PO₃H₂ or phosphoric acid groups—OP(OH)₃.

Examples of monoethylenically unsaturated comonomers comprising acidgroups include monomers comprising —COOH groups, such as acrylic acid ormethacrylic acid, crotonic acid, itaconic acid, maleic acid or fumaricacid, monomers comprising sulfonic acid groups, such as vinylsulfonicacid, allylsulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid,2-methacrylamido-2-methylpropanesulfonic acid,2-acrylamidobutanesulfonic acid, 3-acrylamido-3-methylbutanesulfonicacid or 2-acrylamido-2,4,4-trimethylpentanesulfonic acid, or monomerscomprising phosphonic acid groups, such as vinylphosphonic acid,allylphosphonic acid, N-(meth)acrylamidoalkylphosphonic acids or(meth)acryloyloxyalkylphosphonic acids. Of course the monomers may beused as salts.

The —COOH groups in polyacrylamide-copolymers may not only be obtainedby copolymerizing acrylic amide and monomers comprising —COOH groups butalso by hydrolyzing derivatives of —COOH groups after polymerization.For example, the amide groups —CO—NH₂ of acrylamide may hydrolyze thusyielding —COOH groups.

Also to be mentioned are derivatives of acrylamide thereof, such as, forexample, N-methyl(meth)acrylamide, N,N′-dimethyl(meth)acrylamide, andN-methylolacrylamide, N-vinyl derivatives such as N-vinylformamide,N-vinylacetamide, N-vinylpyrrolidone or N-vinylcaprolactam, and vinylesters, such as vinyl formate or vinyl acetate. N-vinyl derivatives canbe hydrolyzed after polymerization to vinylamine units, vinyl esters tovinyl alcohol units.

Other example comonomers include monomers comprising hydroxy and/orether groups, such as, for example, hydroxyethyl(meth)acrylate,hydroxypropyl(meth)acrylate, allyl alcohol, hydroxyvinyl ethyl ether,hydroxyl vinyl propyl ether, hydroxyvinyl butyl ether orpolyethyleneoxide(meth)acrylates.

Other example comonomers are monomers having ammonium groups, i.emonomers having cationic groups. Examples comprise salts of3-trimethylammonium propylacrylamides or 2-trimethylammoniumethyl(meth)acrylates, for example the corresponding chlorides, such as3-trimethylammonium propylacrylamide chloride (DIMAPAQUAT) and2-trimethylammonium ethyl methacrylate chloride (MADAME-QUAT).

Other example monoethylenically unsaturated monomers include monomerswhich may cause hydrophobic association of the (co)polymers. Suchmonomers comprise besides the ethylenic group and a hydrophilic partalso a hydrophobic part. Such monomers are disclosed for instance in WO2012/069477, which is incorporated herein by reference in its entirety.

Other example comonomers include N-alkyl acrylamides and N-alkylquarternary acrylamides, where the alkyl group comprises, for example, aC2-C28 alkyl group.

In certain embodiments, each of the one or more acrylamide-(co)polymerscan optionally comprise crosslinking monomers, i.e. monomers comprisingmore than one polymerizable group. In certain embodiments, the one ormore acrylamide-(co)polymers may optionally comprise crosslinkingmonomers in an amount of less than 0.5%, or 0.1%, by weight, based onthe amount of all monomers.

In an embodiment, each of the one or more acrylamide-(co)polymerscomprises at least one monoethylenically unsaturated comonomercomprising acid groups, for example monomers which comprise at least onegroup selected from —COOH, —SO₃H or —PO₃H₂. Examples of such monomersinclude but are not limited to acrylic acid, methacrylic acid,vinylsulfonic acid, allylsulfonic acid or2-acrylamido-2-methylpropanesulfonic acid, particularly preferablyacrylic acid and/or 2-acrylamido-2-methylpropanesulfonic acid and mostpreferred acrylic acid or the salts thereof. The amount of suchcomonomers comprising acid groups can be from 0.1% to 70%, from 1% to50%, or from 10% to 50% by weight based on the amount of all monomers.

In an embodiment, each of the one or more acrylamide-(co)polymerscomprise from 50% to 90% by weight of acrylamide units and from 10% to50% by weight of acrylic acid units and/or their respective salts, basedon the total weight of all the monomers making up the copolymer. In anembodiment, each of the one or more acrylamide-(co)polymers comprisefrom 60% to 80% by weight of acrylamide units and from 20% to 40% byweight of acrylic acid units, based on the total weight of all themonomers making up the copolymer.

In some embodiments, the one or more synthetic (co)polymers (e.g., theone or more acrylamide (co)polymers) are in the form of particles, whichare dispersed in the emulsion or LP. In some embodiments, the particlesof the one or more synthetic (co)polymers can have an average particlesize of from 0.4 μm to 5 μm, or from 0.5 μm to 2 μm. Average particlesize refers to the d₅₀ value of the particle size distribution (numberaverage) as measured by laser diffraction analysis.

In some embodiments, the one or more synthetic (co)polymers (e.g., theone or more acrylamide (co)polymers) can have a weight average molecularweight (M_(w)) of from 5,000,000 g/mol to 30,000,000 g/mol; from10,000,000 g/mol to 25,000,000 g/mol; or from 15,000,000 g/mol to25,000,000 g/mol.

In some embodiments, the LP composition can comprise one or moresynthetic (co)polymers (e.g., one or more acrylamide (co)polymers)dispersed in one or more hydrophobic liquids. In these embodiments, theamount of the one or more synthetic (co)polymers (e.g., one or moreacrylamide (co)polymers) in the LP composition can be at least 39% byweight, based on the total weight of the composition. In some of theseembodiments, the amount of the one or more synthetic (co)polymers (e.g.,one or more acrylamide-(co)polymers) in the LP composition can be from39% to 80% by weight, or from 40% to 60% by weight, or from 45% to 55%by weight, based on the total amount of all components of thecomposition (before dilution). In some embodiments, the amount of theone or more synthetic (co)polymers (e.g., one or moreacrylamide-(co)polymers) in the LP composition is 39%, 40%, 41%, 42%,43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%,57%, 58%, 59%, 60%, or higher, by weight, based on the total amount ofall components of the composition (before dilution).

In some embodiments, the LP composition can comprise one or moresynthetic (co)polymers (e.g., one or more acrylamide (co)polymers)emulsified in one or more hydrophobic liquids. In these embodiments, theamount of the one or more synthetic (co)polymers (e.g., one or moreacrylamide (co)polymers) in the LP composition can be less than 38% byweight, less than 35% by weight, or less than 30% by weight based on thetotal weight of the composition. In some of these embodiments, theamount of the one or more synthetic (co)polymers (e.g., one or moreacrylamide-(co)polymers) in the LP composition can be from 10% to 35% byweight, from 10% to 38% by weight, from 15% to 30% by weight, from 15%to 38% by weight, from 20% to 38% by weight, or from 20% to 30% byweight, based on the total amount of all components of the composition(before dilution). In some embodiments, the amount of the one or moresynthetic (co)polymers (e.g., one or more acrylamide-(co)polymers) inthe LP composition is 38%, 37%, 36%, 35%, 34%, 33%, 32%, 31%, 30%, 29%,28%, 27%, 26%, 25%, 24%, 23%, 22%, 21%, 20%, 19%, 18%, 17%, 16%, 15%,14%, 13%, 12%, 11%, or less, by weight, based on the total amount of allcomponents of the composition (before dilution).

Emulsifying Surfactants

In some embodiments, the LP composition can include one or moreemulsifying surfactants. In some embodiments, the one or moreemulsifying surfactants are surfactants capable of stabilizingwater-in-oil-emulsions. Emulsifying surfactants, among other things, inthe emulsion, lower the interfacial tension between the water and thewater-immiscible liquid so as to facilitate the formation of awater-in-oil polymer emulsion. It is known in the art to describe thecapability of surfactants to stabilize water-in-oil-emulsions oroil-in-water emulsions by using the so called “HLB-value”(hydrophilic-lipophilic balance). The HLB-value usually is a number from0 to 20. In surfactants having a low HLB-value the lipophilic parts ofthe molecule predominate and consequently they are usually goodwater-in-oil emulsifiers. In surfactants having a high HLB-value thehydrophilic parts of the molecule predominate and consequently they areusually good oil-in-water emulsifiers. In some embodiments, the one ormore emulsifying surfactants are surfactants having an HLB-value of from2 to 10, or a mixture of surfactant having an HLB-value of from 2 to 10.

Examples of suitable emulsifying surfactants include, but are notlimited to, sorbitan esters, in particular sorbitan monoesters withC12-C18-groups such as sorbitan monolaurate (HLB approx. 8.5), sorbitanmonopalmitate (HLB approx. 7.5), sorbitan monostearate (HLB approx.4.5), sorbitan monooleate (HLB approx. 4); sorbitan esters with morethan one ester group such as sorbitan tristearate (HLB approx. 2),sorbitan trioleate (HLB approx. 2); ethoxylated fatty alcohols with 1 to4 ethyleneoxy groups, e.g. polyoxyethylene (4) dodecylether ether (HLBvalue approx. 9), polyoxyethylene (2) hexadecyl ether (HLB value approx.5), and polyoxyethylene (2) oleyl ether (HLB value approx. 4).

Exemplary emulsifying surfactants include, but are not limited to,emulsifiers having HLB values of from 2 to 10 (e.g., less than 7).Suitable such emulsifiers include the sorbitan esters, phthalic esters,fatty acid glycerides, glycerine esters, as well as the ethoxylatedversions of the above and any other well known relatively low HLBemulsifier. Examples of such compounds include sorbitan monooleate, thereaction product of oleic acid with isopropanolamide, hexadecyl sodiumphthalate, decyl sodium phthalate, sorbitan stearate, ricinoleic acid,hydrogenated ricinoleic acid, glyceride monoester of lauric acid,glyceride monoester of stearic acid, glycerol diester of oleic acid,glycerol triester of 12-hydroxystearic acid, glycerol triester ofricinoleic acid, and the ethoxylated versions thereof containing 1 to 10moles of ethylene oxide per mole of the basic emulsifier. Thus, anyemulsifier can be utilized which will permit the formation of theinitial emulsion and stabilize the emulsion during the polymerizationreaction. Examples of emulsifying surfactants also include modifiedpolyester surfactants, anhydride substituted ethylene copolymers,N,N-dialkanol substituted fatty amides, and tallow amine ethoxylates.

In an embodiment, the inverse emulsion or LP composition comprises from0% to 5% by weight (e.g., from 0.05% to 5%, from 0.1% to 5%, or from0.5% to 3% by weight) of the one or more emulsifying surfactants, basedon the total weight of the composition. These emulsifying surfactantscan be used alone or in mixtures. In some embodiments, the inverseemulsion or LP composition can comprise less than 5% by weight (e.g.,less than 4% by weight, or less than 3% by weight) of the one or moreemulsifying surfactants, based on the total weight of the composition.

Process Stabilizing Agents

In some embodiments, the LP composition can optionally include one ormore process stabilizing agents. The process stabilizing agents aim atstabilizing the dispersion of the particles ofpolyacrylamide-(co)polymers in the organic, hydrophobic phase andoptionally also at stabilizing the droplets of the aqueous monomer phasein the organic hydrophobic liquid before and in course of thepolymerization or processing of the LP composition. The term“stabilizing” means in the usual manner that the agents prevent thedispersion from aggregation and flocculation.

The process stabilizing agents can be any stabilizing agents, includingsurfactants, which aim at such stabilization. In certain embodiments,the process stabilizing agents can be oligomeric or polymericsurfactants. Due to the fact that oligomeric and polymeric surfactantscan have many anchor groups they absorb very strongly on the surface ofthe particles and furthermore oligomers/polymers are capable of forminga dense steric barrier on the surface of the particles which preventsaggregation. The number average molecular weight Mn of such oligomericor polymeric surfactants may for example range from 500 to 60,000 g/mol(e.g., from 500 to 10,000 g/mol, or from 1,000 to 5,000 g/mol). Suitableoligomeric and/or polymeric surfactants for stabilizing polymerdispersions are known to the skilled artisan. Examples of suchstabilizing polymers comprise amphiphilic block copolymers, comprisinghydrophilic and hydrophobic blocks, amphiphilic copolymers comprisinghydrophobic and hydrophilic monomers and amphiphilic comb polymerscomprising a hydrophobic main chain and hydrophilic side chains oralternatively a hydrophilic main chain and hydrophobic side chains.

Examples of amphiphilic block copolymers comprise block copolymerscomprising a hydrophobic block comprising alkylacrylates having longeralkyl chains, e.g., C6 to C22-alkyl chains, such as for instancehexyl(meth)acrylate, 2-ethylhexyl(meth)acrylate, octyl(meth)acrylate,do-decyl(meth)acrylate, hexadecyl(meth)acrylate oroctadecyl(meth)acrylate. The hydrophilic block may comprise hydrophilicmonomers such as acrylic acid, methacrylic acid or vinyl pyrrolidone.

Inverting Surfactants

In some embodiments, the LP composition optionally can include one ormore inverting surfactants. In some embodiments, the one or moreemulsifying surfactants are surfactants which can be used to acceleratethe formation of an inverted composition (e.g., an inverted (co)polymersolution) after mixing the inverse emulsion or LP composition with anaqueous fluid.

Suitable inverting surfactants are known in the art, and include, forexample, nonionic surfactants comprising a hydrocarbon group and apolyalkylenoxy group of sufficient hydrophilic nature. In some cases,nonionic surfactants defined by the general formulaR¹—O—(CH(R²)—CH₂—O)_(n)H (I) can be used, wherein R¹ is aC₈-C₂₂-hydrocarbon group, such as an aliphatic C₁₀-C₁₈-hydrocarbongroup, n is a number of ≥4, preferably ≥6, and R² is H, methyl or ethyl,with the proviso that at least 50% of the groups R² are H. Examples ofsuch surfactants include polyethoxylates based on C₁₀-C₁₈-alcohols suchas C_(12/14)-, C_(14/18)- or C_(16/18)-fatty alcohols, C₁₃- orC_(13/15)-oxoalcohols. The HLB-value can be adjusted by selecting thenumber of ethoxy groups. Specific examples include tridecylalcoholethoxylates comprising from 4 to 14 ethylenoxy groups (e.g.,tridecyalcohol-8 EO (HLB-value approx. 13-14)) or C_(12/14) fattyalcohol ethoxylates (e.g., C_(12/14)·8 EO (HLB-value approx. 13)).Examples of emulsifying surfactants also include modified polyestersurfactants, anhydride substituted ethylene copolymers, N,N-dialkanolsubstituted fatty amides, and tallow amine ethoxylates.

Other suitable inverting surfactants include anionic surfactants, suchas, for example, surfactants comprising phosphate or phosphonic acidgroups.

In some embodiments, the one or more inverting surfactants can comprisepolyoxyethylene sorbitol tetraoleate, C₁₂₋₁₄ branched ethoxylatedalcohol, polyethylene glycol monoleate. In certain embodiments, the oneor more inverting surfactants can comprise from 1 to 20 mole %polyoxyethylene sorbitol tetraoleate, from 60 to 80 mole % C₁₂₋₁₄branched ethoxylated alcohol and about 15 to about 25 mole %polyethylene glycol monoleate.

In some embodiments, the amount of the one or more inverting surfactantsin the inverse emulsion or LP composition is from 1% to 10% (e.g., from1% to 5%) by weight based on the total amount of all components of theinverse emulsion or LP composition.

In certain embodiments, the one or more inverting surfactants can beadded to the inverse emulsion or LP composition directly afterpreparation of the composition comprising the one or more acrylamide(co)polymers dispersed in one or more hydrophobic liquids, andoptionally the one or more emulsifying surfactants (i.e., the inverseemulsion or liquid dispersion polymer composition which is transportedfrom the location of manufacture to the location of use alreadycomprises the one or more inverting surfactants). In another embodimentthe one or more inverting surfactants may be added to the inverseemulsion or LP composition at the location of use (e.g., at an off-shoreproduction site).

Other Components

Optional further components can be added to the inverse emulsion or LPcomposition. Examples of such components comprise radical scavengers,oxygen scavengers, chelating agents, biocides, stabilizers, orsacrificial agents.

Preparation of LP Compositions

LP compositions can be synthesized as according to the followingprocedures.

In a first step, an inverse emulsion (water-in-oil emulsion) ofacrylamide-(co)polymers can be synthesized using procedures known to theskilled artisan. Such inverse emulsions can be obtained by polymerizingan aqueous solution of acrylamide and other comonomers, such aswater-soluble ethylenically unsaturated comonomers, emulsified in ahydrophobic oil phase. In a following step, water within such inverseemulsions can be reduced to an amount of less than 10%, or less than 5%,by weight. Suitable techniques are described for instance in U.S. Pat.Nos. 4,052,353, 4,528,321, or DE 24 19 764 A1, each of which isincorporated herein by reference in its entirety.

For the polymerization, an aqueous monomer solution comprisingacrylamide and optionally other comonomers can be prepared. Acrylamideis a solid at room temperature and aqueous solutions comprising around50% by weight of acrylamide are commercially available. If comonomerswith acidic groups such as acrylic acid are used the acidic groups maybe neutralized by adding aqueous bases such as aqueous sodium hydroxide.The concentration of all monomers together in the aqueous solutionshould usually be from 10% to 60% by weight based on the total of allcomponents of the monomer solution, or from 30% to 50%, or from 35% to45% by weight.

The aqueous solution of acrylamide and comonomers can be emulsified inthe one or more hydrophobic liquids using one or more emulsifyingsurfactants. The one or more emulsifying surfactants may be added to themixture or may be added to the monomer solution or the hydrophobicliquid before mixing. Other surfactants may be used in addition to theone or more emulsifying surfactants, such as a stabilizing surfactant.Emulsifying may be done in the usual manner, e.g. by stirring themixture.

After an emulsion has been formed polymerization may be initiated byadding oil- and/or water soluble initiators for radical polymerizationto the emulsion. The initiators may be dissolved in water or watermiscible organic solvents such as for instance alcohols. It may also beadded as emulsion. Exemplary polymerization initiators comprise organicperoxides such as tert-butyl hydroperoxide, sodium sulfite, sodiumdisulfite or organic sulfites, ammonium- or sodium peroxodisulfate,iron(II) salts or azo groups comprising initiators such as AIBN.

In certain embodiments, one or more chain transfer agents may be addedto the mixture during polymerization. Generally, chain transfer agentshave at least one weak chemical bond, which therefore facilitates thechain transfer reaction. Any conventional chain transfer agent may beemployed, such as propylene glycol, isopropanol, 2-mercaptoethanol,sodium hypophosphite, dodecyl mercaptan, thioglycolic acid, other thiolsand halocarbons, such as carbon tetrachloride. The chain transfer agentis generally present in an amount of from 0.001 percent to 10 percent byweight of the total emulsion, though more may be used.

The polymerization temperature usually is from 30° C. to 100° C., orfrom 30° C. to 70° C., or from 35° C. to 60° C. Heating may be done byexternal sources of heat and/or heat may be generated—in particular whenstarting polymerization—by the polymerization reaction itself.Polymerization times may for example be from about 0.5 h to about 10 h.

The polymerization yields an inverse emulsion comprising an aqueousphase of the one or more acrylamide-(co)polymers dissolved or swollen inwater wherein the aqueous phase is emulsified in an organic phasecomprising the one or more hydrophobic liquids.

In order to convert the inverse emulsion obtained to the LP compositionsto be used in the methods described herein, after the polymerization,some or all of the water is distilled off from the emulsion thusyielding particles of the one or more acrylamide-(co)polymers emulsifiedin the one or more hydrophobic liquids.

For the liquid polymer compositions, the water is at least removed to alevel of less than 10%, or less than 7%, or less than 5%, or less than3% by weight. In exemplary embodiments, the removal of water is carriedout by any suitable means, for example, at reduced pressure, e.g. at apressure of 30 hPa to 500 hPa, preferably 50 hPa to 250 hPa. Thetemperature in course of water removal may typically be from 70° C. to100° C., although techniques which remove water at higher temperaturesmay be used. In certain embodiments, one or more of the hydrophobicliquids used in the inverse emulsion may be a low boiling liquid, whichmay distill off together with the water as a mixture.

After removal of the amount of water desired, the one or more invertingsurfactants, and other optional components, can be added.

In some embodiments, the manufacture of the liquid polymer compositionsis carried out in a chemical production plant.

Inverted Polymer Solutions

Also provided herein are inverted polymer solutions, as well as methodsof preparing the inverted polymer solutions from the LP compositionsdescribed herein and methods for using the inverted polymer solutions inoil and gas operations.

Methods for preparing inverted polymer solutions from the LPcompositions described herein can comprise inverting the LP compositionin an aqueous fluid to provide an inverted polymer solution having aconcentration of one or more synthetic (co)polymers (e.g., one or moreacrylamide (co)polymers) of from 50 to 15,000 ppm.

In some embodiments, the inverted polymer solution can have aconcentration of one or more synthetic (co)polymers (e.g., one or moreacrylamide (co)polymers) of at least 50 ppm (e.g., at least 100 ppm, atleast 250 ppm, at least 500 ppm, at least 750 ppm, at least 1000 ppm, atleast 1500 ppm, at least 2000 ppm, at least 2500 ppm, at least 3000 ppm,at least 3500 ppm, at least 4000 ppm, at least 4500 ppm, at least 5000ppm, at least 5500 ppm, at least 6000 ppm, at least 6500 ppm, at least7000 ppm, at least 7500 ppm, at least 8000 ppm, at least 8500 ppm, atleast 9000 ppm, at least 9500 ppm, at least 10,000 ppm, at least 10,500ppm, at least 11,000 ppm, at least 11,500 ppm, at least 12,000 ppm, atleast 12,500 ppm, at least 13,000 ppm, at least 13,500 ppm, at least14,000 ppm, or at least 14,500 ppm).

In some embodiments, the inverted polymer solution can have aconcentration of one or more synthetic (co)polymers (e.g., one or moreacrylamide (co)polymers) of 15,000 ppm or less (e.g., 14,500 ppm orless, 14,000 ppm or less, 13,500 ppm or less, 13,000 ppm or less, 12,500ppm or less, 12,000 ppm or less, 11,500 ppm or less, 11,000 ppm or less,10,500 ppm or less, 10,000 ppm or less, 9,500 ppm or less, 9,000 ppm orless, 8,500 ppm or less, 8,000 ppm or less, 7,500 ppm or less, 7,000 ppmor less, 6,500 ppm or less, 6,000 ppm or less, 5,500 ppm or less, 5,000ppm or less, 4500 ppm or less, 4000 ppm or less, 3500 ppm or less, 3000ppm or less, 2500 ppm or less, 2000 ppm or less, 1500 ppm or less, 1000ppm or less, 750 ppm or less, 500 ppm or less, 250 ppm or less, or 100ppm or less).

The inverted polymer solution can have a concentration of one or moresynthetic (co)polymers (e.g., one or more acrylamide (co)polymers)ranging from any of the minimum values described above to any of themaximum values described above. For example, in some embodiments, theinverted polymer solution can have a concentration of one or moresynthetic (co)polymers (e.g., one or more acrylamide (co)polymers) offrom 500 to 5000 ppm (e.g., from 500 to 3000 ppm, or from 500 to 1500ppm).

In some embodiments, the inverted polymer solution can be an aqueousunstable colloidal suspension. In other embodiments, the invertedpolymer solution can be an aqueous stable solution.

In some embodiments, the inverted polymer solution can have a filterratio of 1.5 or less (e.g., 1.45 or less, 1.4 or less, 1.35 or less, 1.3or less, 1.25 or less, 1.2 or less, 1.15 or less, 1.1 or less, or lessthan 1.05) at 15 psi using a 1.2 μm filter. In some embodiments, theinverted polymer solution can have a filter ratio of greater than 1(e.g., at least 1.05, at least 1.1, at least 1.15, at least 1.2, atleast 1.25, at least 1.3, at least 1.35, at least 1.4, or at least 1.45)at 15 psi using a 1.2 μm filter.

The inverted polymer solution can a filter ratio at 15 psi using a 1.2μm filter ranging from any of the minimum values described above to anyof the maximum values described above. For example, in some embodiments,the inverted polymer solution can have a filter ratio of from 1 to 1.5(e.g., from 1.1 to 1.4, or from 1.1 to 1.3) at 15 psi using a 1.2 μmfilter.

In certain embodiments, the inverted polymer solution can have aviscosity based on shear rate, temperature, salinity, polymerconcentration, and polymer molecular weight. In some embodiments, theinverted polymer solution can have a viscosity of from 2 cP to 100 cP,where the 2 cP to 100 cP is an output using the ranges in the followingtable:

Polymer viscosity (cP) 2~100 Shear rate (1/sec) 0.1~1000  Temperature (°C.) 1~120 Salinity (ppm)    0~250,000 Polymer concentration (ppm)  50~15,000 Polymer molecular weight (Dalton) 2M~26M 

In some embodiments, the inverted polymer solution can have a viscosityof from 25 cP to 35 cP at 30° C. In some embodiments, the invertedpolymer solution can have a viscosity of greater than 10 cP at 40° C. Incertain embodiments, the inverted polymer solution can have a viscosityof from 20 cP to 30 cP at 40° C.

In some embodiments, when the LP composition is inverted in an aqueousfluid, providing an inverted polymer solution having from 50 to 15,000ppm, from 500 to 5,000 ppm, or from 500 to 3000 ppm, active polymer, theinverted polymer solution has a viscosity of at least 20 cP at 40° C.,and a filter ratio (FR) (1.2 micron filter) of 1.5 or less. In certainembodiments, when the LP composition is inverted in an aqueous fluid,providing an inverted polymer solution having from 50 to 15,000 ppm,from 500 to 5000 ppm, or from 500 to 3000 ppm, active polymer, theinverted polymer solution has a viscosity of at least 20 cP at 30° C.,and a filter ratio (FR) (1.2 micron filter) of 1.5 or less. As usedherein, “inverted” refers to the point at which the viscosity of theinverted polymer solution has substantially reached a consistentviscosity. In practice, this may be determined for example by measuringviscosity of the inverted polymer solution periodically over time andwhen three consecutive measurements are within the standard of error forthe measurement, then the composition is considered inverted. In someembodiments, inversion of the LP forms the inverted polymer solution in30 minutes or less (e.g., 15 minutes or less, 10 minutes or less, 5minutes or less, or less).

As described above, methods for preparing an inverted polymer solutionfrom the LP composition described herein can comprise inverting the LPcomposition in an aqueous fluid to provide an inverted polymer solutionhaving a concentration of acrylamide (co)polymer of from 50 to 15,000ppm. Inversion of the LP composition can be performed as a batch processor a continuous process. In certain embodiments, inversion of the LPcomposition can be performed as a continuous process. For example,inversion of the LP composition can be performed as a continuous processto produce a fluid stream for injection into a hydrocarbon-bearingformation. A continuous process is a process that can be effectedwithout the need to be intermittently stopped or slowed. For example,continuous processes can meet one or more of the following criteria: (a)materials for forming the inverted polymer solution (e.g., the LPcomposition and the aqueous fluid) are fed into the system in which theinverted polymer solution is produced at the same rate as the invertedpolymer solution is removed from the system; (b) the nature of thecomposition(s) introduced to the system in which the inverted polymersolution is produced is a function of the composition(s) position withthe process as it flows from the point at which the composition(s) areintroduced to the system to the point at which the inverted polymersolution is removed from the system; and/or (c) the quantity of invertedpolymer solution produced is a function of (i) the duration for whichthe process is operated and (ii) the throughput rate of the process.

Inversion of the LP composition can comprise a single step, or aplurality of steps (i.e., two or more steps). In some embodiments,inversion of the LP composition can be performed in a single step. Inthese embodiments, the LP composition (e.g., a composition having atleast 39% (e.g., 39% or more) by weight of one or more synthetic(co)polymers (e.g., one or more acrylamide (co)polymers) dispersed in ahydrophobic liquid, or a composition having up to 35% (e.g., less than35%) by weight of one or more synthetic (co)polymers (e.g., one or moreacrylamide (co)polymers) emulsified in a hydrophobic liquid) can beinverted in an aqueous fluid to provide an inverted polymer solutionhaving a concentration of one or more synthetic (co)polymers (e.g., oneor more acrylamide (co)polymers) of from 50 to 15,000 ppm.

The single inversion step can comprise diluting the LP composition inthe aqueous fluid in an in-line mixer to provide the inverted polymersolution. For example, a polymer feed stream comprising the LPcomposition can be combined (e.g., in a fixed ratio) with an aqueousfluid stream upstream of an in-line mixer. The combined fluid stream canthen pass through the in-line mixer, emerging as the inverted polymersolution. In some embodiments, the in-line mixer can have a mixer inletand a mixer outlet, and the difference in pressure between the mixerinlet and the mixer outlet is from 15 psi to 400 psi (e.g., from 15 psito 150 psi, from 15 psi to 100 psi, or from 15 psi to 75 psi).

An example system for inversion of LP compositions in a single step isillustrated schematically in FIG. 1. As shown in FIG. 1, a pump 102 canbe used to inject a stream of the LP composition 104 into a line 106carrying the aqueous fluid stream. The combined fluid stream can thenpass through an in-line mixer 108 having a mixer inlet 110 and a mixeroutlet 112, emerging as the inverted polymer solution. The pressure dropthrough the in-line mixer 108 (Δp) can be from 15 psi to 400 psi (e.g.,from 15 psi to 150 psi, from 15 psi to 100 psi, or from 15 psi to 75psi).

In other embodiments, inversion of the LP composition can be performedin two or more steps (e.g., an inversion step in which the LPcomposition is inverted in the aqueous fluid to form a concentratedpolymer composition having a polymer concentration of up to 15,000 ppm;and one or more dilution steps in which the concentrated polymercomposition is diluted in the aqueous fluid to provide the invertedpolymer solution. For example, inversion of the LP composition can beperformed in two, three, four, five, or more consecutive steps. Incertain cases, inversion of the LP composition can be performed in twosteps. In these embodiments, inversion of the LP can comprise as a firststep, inverting the LP composition in an aqueous fluid in a firstin-line mixer having a first mixer inlet and a first mixer outlet toprovide an inverted polymer solution with a concentration of synthetic(co)polymer (e.g., acrylamide (co)polymer) that is up to 15,000 ppm(e.g., from 5,000 to 15,000 ppm); and as a second step, diluting theinverted polymer solution in the aqueous fluid in a second in-line mixerhaving a second mixer inlet and a second mixer outlet to provide theinverted polymer solution.

For example, a polymer feed stream comprising the LP composition can becombined (e.g., in a fixed ratio) with an aqueous fluid stream upstreamof a first in-line mixer. The combined fluid stream can then passthrough the first in-line mixer, emerging as an inverted polymersolution with a concentration of synthetic (co)polymer (e.g., acrylamide(co)polymer) that is up to 15,000 ppm (e.g., from 5,000 to 15,000 ppm).The fluid stream can then be combined (e.g., in a fixed ratio) with asecond aqueous fluid stream upstream of a second in-line mixer. Thecombined fluid stream can then pass through the second in-line mixer,emerging as the inverted polymer solution. In some embodiments, thefirst in-line mixer can have a first mixer inlet and a first mixeroutlet, and the difference in pressure between the first mixer inlet andthe first mixer outlet can be from 15 psi to 400 psi (e.g., from 15 psito 150 psi, from 15 psi to 100 psi, or from 15 psi to 75 psi). In someembodiments, the second in-line mixer can have a second mixer inlet anda second mixer outlet, and the difference in pressure between the secondmixer inlet and the second mixer outlet can be from 15 psi to 400 psi(e.g., from 15 psi to 150 psi, from 15 psi to 100 psi, or from 15 psi to75 psi).

An example system for inversion of LP compositions in two steps isillustrated schematically in FIG. 2. As shown in FIG. 2, a pump 102 canbe used to inject a stream of the LP composition 104 into bypass 101mounted on main line 103 carrying the aqueous fluid stream. A valve 105positioned on main line 103 downstream of bypass 101 can be used todirect aqueous fluid flow through bypass 101. The combined fluid streamcan then pass through a first in-line mixer 108 having a first mixerinlet 110 and a first mixer outlet 112, emerging as the inverted polymersolution with a concentration of synthetic (co)polymer (e.g., acrylamide(co)polymer) that is up to 15,000 ppm (e.g., from 5,000 to 15,000 ppm).The pressure drop through the first in-line mixer 108 (Δp1) can be from15 psi to 400 psi (e.g., from 15 psi to 150 psi, from 15 psi to 100 psi,or from 15 psi to 75 psi). The inverted polymer fluid stream 114 canthen be combined (e.g., in a fixed ratio) with the aqueous fluid streamin main line 103 upstream of a second in-line mixer 116. The combinedfluid stream can then pass through a second in-line mixer 116 having asecond mixer inlet 118 and a second mixer outlet 120, emerging as theinverted polymer solution. The pressure drop through the second in-linemixer 116 (Δp2) can be from 15 psi to 400 psi (e.g., from 15 psi to 150psi, from 15 psi to 100 psi, or from 15 psi to 75 psi).

The LP compositions described herein can also be inverted usinginversion methods and systems known in the art, such as those describedin U.S. Pat. No. 8,383,560, which is hereby incorporated by reference inits entirety.

Another example system for inversion of LP compositions is illustratedschematically in FIG. 3. As shown in FIG. 3A, a pump 102 can be used todirect a stream of the LP composition 104 to LP manifold 122. LPmanifold 122 can include an LP manifold inlet 124 through which the LPcomposition enters the LP manifold 122, and a plurality of LP manifoldoutlets 126 (in this example three manifold outlets) through whichstreams of the LP composition exit the LP manifold 122. The system canalso include a main line 103 carrying an aqueous fluid stream to aqueousfluid manifold 128. The aqueous fluid manifold 128 can include anaqueous fluid manifold inlet 130 through which the aqueous fluid entersthe aqueous fluid manifold 128, and a plurality of aqueous fluidmanifold outlets 132 (in this example three manifold outlets) throughwhich streams of the aqueous fluid exit the aqueous fluid manifold 128.Each stream of LP composition exiting LP manifold 122 can then becombined with a stream of aqueous fluid exiting the aqueous fluidmanifold 128 in a different configuration of in-line mixers 134, therebyforming a plurality of streams of the inverted polymer solution inparallel. The configuration of in-line mixers 134 for inversion of theLP composition comprises parallel single steps, parallel multiple steps,or any combination thereof. FIG. 3B shows one example of configurationof the in-line mixers 134 comprises the combination of two single stepsand one two-step of inversion process in parallel.

Any suitable in-line mixer(s) can be used in conjunction with theinversion methods described above. The in-line mixer can be a dynamicmixer or a static mixer. Suitable dynamic mixers, which involvemechanical agitation of one type or another, are known in the art, andinclude impeller mixers, turbine mixers, rotor-stator mixers, colloidmills, pumps, and pressure homogenizers. In certain embodiment, thein-line mixer(s) can comprise a dynamic mixer such as an electricalsubmersible pump, hydraulic submersible pump, or a progressive cavitypump. In certain embodiments, the in-line mixer(s) can comprise staticmixers. Static mixers are mixers that mix fluids in flow without the useof moving parts. Static mixers are generally constructed from a seriesof stationary, rigid elements that form intersecting channels to split,rearrange and combine component streams resulting in one homogeneousfluid stream. Static mixers provide simple and efficient solutions tomixing and contacting problems. More affordable than dynamic agitatorsystems, static mixing units have a long life with minimal maintenanceand low pressure drop. Static mixers can be fabricated from metalsand/or plastics to fit pipes and vessels of virtually any size andshape. In some cases, the static mixer can comprise a region of pipe,for example a serpentine region of pipe that facilitates mixing.

The aqueous fluid used to invert the LP composition can comprise from 0to 250,000 ppm; 15,000 to 160,000 ppm; from 15,000 to 100,000 ppm; from10,000 to 50,000 ppm; from 15,000 to 50,000 ppm; from 30,000 to 40,000ppm; from 10,000 to 25,000 ppm; from 10,000 to 20,000 ppm; or from15,000 to 16,000 ppm total dissolved solids (tds). In an exampleembodiment, the aqueous fluid can comprise a brine having about 15,000ppm tds. In one embodiment, the brine may be a synthetic seawater brineas illustrated in Table 1.

TABLE 1 Composition of an example synthetic seawater brine. Ions (ppm)Synthetic seawater brine Na+ 10800 K+ 400 Ca++ 410 Mg++ 1280 Cl− 19400TDS 32290

The aqueous fluid used to invert the LP compositions can compriseproduced reservoir brine, reservoir brine, sea water, fresh water,produced water, water, saltwater (e.g. water containing one or moresalts dissolved therein), brine, synthetic brine, synthetic seawaterbrine, or any combination thereof. Generally, the aqueous fluid cancomprise water from any readily available source, provided that it doesnot contain an excess of compounds that may adversely affect othercomponents in the inverted polymer solution or render the invertedpolymer solution unsuitable for its intended use (e.g., unsuitable foruse in an oil and gas operation such as an EOR operation). If desired,aqueous fluids obtained from naturally occurring sources can be treatedprior to use. For example, aqueous fluids can be softened (e.g., toreduce the concentration of divalent and trivalent ions in the aqueousfluid) or otherwise treated to adjust their salinity. In certainembodiments, the aqueous fluid can comprise soft brine or hard brine. Incertain embodiments, the aqueous fluid can comprise produced reservoirbrine, reservoir brine, sea water, or a combination thereof.

In one embodiment, seawater is used as the aqueous fluid, sinceoff-shore production facilities tend to have an abundance of seawateravailable, limited storage space, and transportation costs to and froman off-shore site are typically high. If seawater is used as the aqueousfluid, it can be softened prior to the addition of the suspendedpolymer, thereby removing multivalent ions in the water (e.g.,specifically Mg²⁺ and Ca²⁺).

In some embodiments, the aqueous fluid can have a temperature of from 1°C. to 120° C. In other embodiments, the aqueous fluid can have atemperature of from 45° C. to 95° C.

The inversion methods described herein can be specifically adapted foruse in a particular oil and gas operation. For example, in someembodiments, inversion of the LP can be performed as a continuousprocess to produce a fluid stream for injection into ahydrocarbon-bearing formation.

In some cases, the in-line mixer (or one or more in-line mixers in thecase of multistep inversion methods) can be arranged downstream frompumping equipment at the surface (e.g., on land, on a vessel, or on anoffshore platform) that pumps the LP composition and the aqueous fluid.In certain embodiments, the in-line mixer (or one or more in-line mixersin the case of multistep inversion methods) can be positioned at or nearthe wellhead of a well. In certain embodiments, the in-line mixer can bearranged downhole. In certain embodiments, the in-line mixer (or one ormore in-line mixers in the case of multistep inversion methods) can bepositioned subsurface, subsea, or downhole.

In certain embodiments, the hydrocarbon-bearing formation can be asubsea reservoir. In these embodiments, the in-line mixer (or one ormore in-line mixers in the case of multistep inversion methods) can bearranged downstream from pumping equipment at the surface (e.g., onshore, on a vessel, or on an offshore platform) that pumps the LPcomposition and/or the aqueous fluid. In certain embodiments, thein-line mixer (or one or more in-line mixers in the case of multistepinversion methods) can be positioned subsea. Thus, depending on the oiland gas operation, for example, an in-line mixer can be positioned onthe surface, subsurface, subsea, or downhole.

In some embodiments, the in-line mixer can be part of an in-line polymerdump flood injection system. Referring now to FIG. 4, in certain exampleembodiments, the in-line polymer dump flood injection system 200 can beused in a formation having a source reservoir layer 202, dividing orimpermeable layers 204, and a target reservoir layer 206. The dividingor impermeable layers 204 can include shale, a combination of shales andsmaller source reservoirs, gas reservoirs, or other oil reservoirs. Incertain example embodiments, an injection well 208 is formed in aninjection zone and completed with a casing 210. The injection well 208is further completed by installing the injection system 200 therewithin.In certain example embodiments, the injection system 200 includes awater injection tubing 212 through which the aqueous fluid can beprovided, a chemical injection tubing 214 through which LP compositioncan be provided, and a static mixer 228. Furthermore, in certain exampleembodiments, the injection well 208 is separated into a water collectionzone 222, a mixing zone 224, and an injection zone 226. In certainexample embodiments, the water collection zone 222 is substantiallyaligned with the source reservoir layer 202 of the formation, theinjection zone 226 is substantially aligned with the target reservoirlayer 206 of the formation, and the mixing zone 224 is disposed inbetween the water collection zone 222 and the injection zone 226.

In certain example embodiments, such as the example embodimentillustrated in FIG. 4, the water collection zone 222 is isolated betweena first packer 218 disposed on top of the water collection zone 222 anda second packer 220 disposed between the water collection zone 222 andthe mixing zone 224. In certain example embodiments, the water injectiontubing 212 extends from the surface, where it is connected to a tubingstring, and into the mixing zone 224, traversing the first packer 218and the second packer 220. Accordingly, the tubing string is in fluidcommunication with the mixing zone 224. In certain example embodiments,the first packer 218 and second packer 220 are sealed around the waterinjection tubing 212. In certain example embodiments, the waterinjection tubing 212 and the casing 210 of the injection well 208include a plurality of perforations 230, which put the water injectiontubing 212 in fluid communication with the source reservoir layer 202.Water from the source reservoir layer 202 flows into the watercollection zone through the perforations 230 in the casing 210 and theninto the water injection tubing 212 through the perforations 230 in thewater injection tubing 212. The water is then delivered into the mixingzone 224 via the water injection tubing 212. In certain exampleembodiments, the water injection tubing 212 is coupled to a pump 216,which facilitates the pulling of water out of the source reservoir layer202 and the injection of water into the mixing zone 224. In certainexample embodiments, the pump 216 controls the rate of water flow intothe mixing zone 224.

In certain example embodiments, the chemical injection tubing 214extends from the surface through to and terminating in the mixing zone224. The chemical injection tubing 214 is coupled to a tubing stringthrough which the LP composition can be delivered downhole and into themixing zone 224. In certain example embodiments, the chemical injectiontubing 214 traverses the first packer 218 and the second packer 220 suchthat the first packer 218 and the second packer 220 form a seal aroundthe chemical injection tubing 214. In certain example embodiments, thechemical injection tubing 214 traverses the water collection zone 222while the inside of the chemical injection tubing 214 is isolated fromthe water collection zone 222. In certain example embodiments, duringoperation, an LP composition is pumped into the mixing zone 224 from thesurface via the chemical injection tubing 214. In certain exampleembodiments, the LP composition is pumped into the mixing zone 224 at acontrolled rate. In certain example embodiments, the LP composition ispumped into the mixing zone 224 at a set ratio with respect to the water(i.e., the aqueous fluid) pumped into the mixing zone 224 via the waterinjection tubing 212, such that the LP composition is inverted in mixingzone 224, thereby forming an inverted polymer solution.

In certain example embodiments, when the water and the LP compositionare injected into the mixing zone 224, the water and the LP compositionare forced to travel through the static mixer 228. In certain exampleembodiments, the static mixer 228 provides a path having a plurality ofobstacles which force fluid traveling therethrough to take a windingpath. Thus, when water and LP composition are forced through the staticmixer 228 together, the water and LP composition are mixed together, andexit the static mixer 228 as an inverted polymer solution.

In certain example embodiments, the inverted polymer solution is theninjected into the injection zone 226 and ultimately injected into thesurrounding target reservoir 206 via perforations 230 in the casing 210.The injection fluid injected into the target reservoir 206 increases thepressure in the target reservoir 206. This mobilizes hydrocarbons in thetarget reservoir and pushes the hydrocarbons towards a neighboringproducing well, where the hydrocarbons are can be recovered.

FIG. 5 illustrates a second example embodiment of an in-line polymerdump flood injection system. Elements that are the same or comparable tothe elements illustrated in the example shown in FIG. 4 are identifiedby the same reference number in FIGS. 4-9. Similar to the exampleillustrated in FIG. 4, the injection system 300 is installed within acased injection well 208 having a source reservoir layer 202 and atarget reservoir layer 206. In certain example embodiments, theinjection well 208 is separated into the water collection zone 222, themixing zone 224, and the injection zone 226. In certain exampleembodiments, the injection system 300 includes a water collection tubing302, a water injection tubing 304, an electrical submersible pump (ESP)306, a chemical injection tubing 308, and a static mixer 328. In certainexample embodiments, the water collection zone 222 is isolated between afirst packer 218 disposed on top of the water collection zone 222 and asecond packer 220 disposed between the water collection zone 222 and themixing zone 224. In certain example embodiments, the water collectiontubing 302 extends from the water collection zone 222 to the ESP 306,which is located above the water collection zone 222. The waterinjection tubing 304 is disposed within the water collection tubing 302and extends from the ESP 306 to the mixing zone 224, traversing thefirst packer 218 and the second packer 220. In certain exampleembodiments, water flows into the water collection zone 222 from thesource reservoir 202 via a plurality of perforations 230 formed in thecasing 210 of the injection well 208. The water is drawn into the ESP306 through the water collection tubing 302, and then injected into themixing zone 224 through the water injection tubing 304. The ESP 306 canbe used to control the rate of water (i.e., aqueous fluid) injected intothe mixing zone 224.

In certain example embodiments, the chemical injection tubing 308extends from the surface through to and terminating in the mixing zone224. The chemical injection tubing 308 is coupled to a tubing stringthrough which an LP composition can be delivered downhole and into themixing zone 224. In certain example embodiments, the chemical injectiontubing 308 traverses the first packer 218 and the second packer 220 suchthat the first packer 218 and the second packer 220 form a seal aroundthe chemical injection tubing 308. In certain example embodiments, thechemical injection tubing 308 traverses the water collection zone 222while the inside of the chemical injection tubing 308 is isolated fromthe water collection zone 222. Thus, the LP composition is isolated fromthe ESP 306. In certain example embodiments, the LP composition ispumped into the mixing zone 224 at a controlled rate. In certain exampleembodiments, the LP composition is pumped into the mixing zone 224 at aset ratio with respect to the water (i.e., aqueous fluid) pumped intothe mixing zone 224 via the water injection tubing 304 and ESP 306, suchthat the LP composition is inverted in mixing zone 224, thereby formingan inverted polymer solution.

In certain example embodiments, when the water and the LP compositionare injected into the mixing zone 224, the water and the LP compositionare forced to travel through the static mixer 328. When water and LPcomposition are forced through the static mixer 328 together, the waterand LP composition are mixed together, and exit the static mixer 228 asan inverted polymer solution.

In certain example embodiments, the inverted polymer solution is theninjected into the injection zone 226 and ultimately injected into thesurrounding target reservoir 206 via perforations 230 in the casing 210.The injection fluid injected into the target reservoir 206 increases thepressure in the target reservoir 206. This mobilizes hydrocarbons in thetarget reservoir and pushes the hydrocarbons towards a neighboringproducing well, where the hydrocarbons are can be recovered.

FIG. 6 illustrates a third example embodiment of an in-line polymer dumpflood injection system. In certain example embodiments, the injectionsystem 400 includes a progressive cavity pump (PCP) 402, a chemicalinjection tubing 404, and a static mixer 406. In certain exampleembodiments, the water collection zone 222 is isolated between a firstpacker 218 disposed on top of the water collection zone 222 and a secondpacker 220 disposed between the water collection zone 222 and the mixingzone 224. In certain example embodiments, water flows into the watercollection zone 222 from the source reservoir 202 via perforations 230formed in the casing 210 of the injection well 208. The PCP 402 extendsfrom the water collection zone 222 to the mixing zone 224, traversingthe second packer 220. In certain example embodiments, the PCP 402drives water from the water collection zone 222 into the mixing zone224. The water collection zone 222 and the mixing zone 224 are otherwiseisolated from each other. In one embodiment, the PCP 402 can include astator and a drive rod, as well as an inlet towards the top of the PCP402 and an outlet towards the bottom of the PCP 402. The water from thewater collection zone 222 enters the PCP 402 through the inlet of thePCP 402 and the water exits through the outlet of the PCP 402. Thus, thePCP 402 can be used to control the rate of water (i.e., aqueous fluid)injected into the mixing zone 224.

In certain example embodiments, the chemical injection tubing 404extends from the surface through to and terminating in the mixing zone224. The chemical injection tubing 404 is coupled to a tubing stringthrough which an LP composition is delivered downhole and into themixing zone 224. In certain example embodiments, the chemical injectiontubing 404 traverses the first packer 218 and the second packer 220 suchthat the first packer 218 and the second packer 220 form a seal aroundthe chemical injection tubing 404. In certain example embodiments, thechemical injection tubing 404 traverses the water collection zone 222while the inside of the chemical injection tubing 404 is isolated fromthe water collection zone 222. Thus, the LP composition is isolated fromthe PCP 402. In certain example embodiments, the LP composition ispumped into the mixing zone 224 at a controlled rate. In certain exampleembodiments, the LP composition is pumped into the mixing zone 224 at aset ratio with respect to the water (i.e., aqueous fluid) pumped intothe mixing zone 224 via the PCP 402, such that the LP composition isinverted in mixing zone 224, thereby forming an inverted polymersolution.

In certain example embodiments, when the water and the LP compositionare injected into the mixing zone 224, the water and the LP compositionare forced to travel through the static mixer 406. When water and LPcomposition are forced through the static mixer 406 together, the waterand LP composition are mixed together, and exit the static mixer 406 asan inverted polymer solution.

In certain example embodiments, the inverted polymer solution is theninjected into the injection zone 226 and ultimately injected into thesurrounding target reservoir 206 via perforations formed in the casing210.

FIG. 7 illustrates a fourth example embodiment of an in-line polymerdump flood injection system. In certain example embodiments, theinjection system 500 is installed in an injection well 208 which isseparated into a water collection zone 222 and an injection zone 226. Incertain example embodiments, the water collection zone 222 is isolatedbetween a first packer 218 disposed on top of the water collection zone222 and a second packer 220 disposed between the water collection zone222 and the injection zone 226. In certain example embodiments, theinjection system 500 includes a water collection tubing 504, a waterinjection tubing 506, an ESP 502, a chemical injection tubing 512, and astatic mixer 510. In certain example embodiments, the chemical injectiontubing 512 extends from the surface to the ESP 502, and the chemicalinjection tubing 512 does not traverse the first packer 218. Forexample, the chemical injection tubing 512 is coupled to a tubing stringthrough which an LP composition is delivered downhole and into the ESP502. In certain example embodiments, water (i.e., aqueous fluid) flowsinto the water collection zone 222 from the source reservoir 202 via aplurality of perforations 230 formed in the casing 210 of the injectionwell 208. In certain example embodiments, the water collection tubing504 extends from the water collection zone 222 to the ESP 502, which islocated above the water collection zone 222. The water injection tubing506 is disposed partially within the water collection tubing 504 andextends from the ESP 502 to the injection zone 226, traversing the firstpacker 218 and the second packer 220. The water (i.e., aqueous fluid) isdrawn into the ESP 502 through the water collection tubing 504 and theLP composition is drawn into the ESP 502 through the chemical injectiontubing 512, and then injected into the injection zone 226 through thewater injection tubing 506. In certain example embodiments, a staticmixer 510 is disposed within the water injection tubing 506, such thatthe water (i.e., aqueous fluid) and LP composition are mixed together asthey travel through the water injection tubing 506 and into theinjection zone 226, where they exit as an inverted polymer solution. TheESP 502 can be used to control the rate of water and LP compositioninjected into the injection zone 226. In certain example embodiments,the water injection tubing 506 includes a flow meter 508 which monitorsflow rate. In certain example embodiments, the inverted polymer solutionis then injected into the injection zone 226 and ultimately injectedinto the surrounding target reservoir 206 via perforations formed in thecasing 210.

FIG. 8 illustrates a fifth example embodiment of an in-line polymer dumpflood injection system. In certain example embodiments, the injectionsystem 600 is installed in an injection well 208 which is separated intoa water collection zone 222 and an injection zone 226. In certainexample embodiments, the water collection zone 222 is isolated between afirst packer 218 disposed on top of the water collection zone 222 and asecond packer 220 disposed between the water collection zone 222 and theinjection zone 226. In certain example embodiments, the injection system600 includes a chemical injection tubing 602, a PCP 604, and a staticmixer 606. The PCP 604 can include a stator and a drive rod, as well asan inlet towards the top of the PCP 604 and an outlet towards the bottomof the PCP 604. In certain example embodiments, water (i.e., aqueousfluid) flows into the water collection zone 222 from the sourcereservoir 202 via perforations 230 formed in the casing 210 of theinjection well 208. The chemical injection tubing 602 extends into thewater collection zone 222 from the surface. The PCP 604 is coupled tothe chemical injection tubing 602. In certain example embodiments, oneway valves 610, 612 are disposed at the junction of the chemicalinjection tubing 602 and the PCP 604, and the one way valves 610, 612allow water to enter the PCP 604 from the water collection zone 222. Theone way valves 610, 612 are meant to allow water from the watercollection zone 222 to pass through the one way valves 610, 612 (andtowards the PCP 604), but the LP composition does not pass through theone way valves 610, 612 into the water collection zone 222. The waterthat passes through the one way valves 610, 612 and the LP compositionfrom the chemical injection tubing 602 are pumped downward through thePCP 604. For example, the water from the water collection zone 222 andthe LP composition from the chemical injection tubing 602 enter the PCP604 through the inlet of the PCP 604 and exit through the outlet of thePCP 604 into the static mixer 606. The static mixer 606 is coupled tothe PCP 604 opposite the chemical injection tubing 602. Thus, the water(i.e., aqueous fluid) and LP composition are driven into the staticmixer 606 by the PCP 604, where they are mixed together, and exit thestatic mixer 606 as an inverted polymer solution.

In certain example embodiments, the inverted polymer solution is theninjected into the injection zone 226 and ultimately injected into thesurrounding target reservoir 206 via perforations 230 formed in thecasing 210.

FIG. 9 illustrates a sixth example embodiment of an inline chemical dumpflood injection system. In certain example embodiments, the injectionsystem 700 is installed in an injection well 208 which is separated intoa water collection zone 222 and an injection zone 226. In certainexample embodiments, the water collection zone 222 is isolated between afirst packer 218 disposed on top of the water collection zone 222 and asecond packer 220 disposed between the water collection zone 222 and theinjection zone 226. In certain example embodiments, the injection system700 includes a chemical injection tubing 702 and a static mixer 706. Incertain example embodiments, the chemical injection tubing 702 alsoincludes a flow meter for measuring flow rate. The chemical injectiontubing 702 extends from the surface and into the injection zone 226. Incertain example embodiments, water flows into the water collection zone222 from the source reservoir 202 via perforations 230 formed in thecasing 210 of the injection well 208. The source reservoir 202 has aparticular pressure illustrated as P1. In certain example embodiments,the chemical injection tubing 702 also includes a plurality ofperforations 230 which allows water to flow into the chemical injectiontubing 702. A LP composition with a particular pressure illustrated asP2 is pumped into the chemical injection tubing 702 from the surface.The water (i.e., aqueous fluid) and the LP composition flow into thestatic mixer 706, where they are mixed together, and exit the staticmixer 706 as an inverted polymer solution. The inverted polymer solutionis then injected into the injection zone 226 and ultimately injectedinto the surrounding target reservoir 206 via perforations 230 formed inthe casing 210. The target reservoir 206 has a particular pressureillustrated as P3. As explained further below, the pressure differencesbetween P1, P2, and P3 drive the water, the LP composition, or both totheir destinations.

In FIG. 9, the pressure differences between P1, P2, and P3 drive thewater, the LP composition, or both to their destinations. For example,in some cases, the pressure of the source reservoir 202 is higher thanthe pressure of the LP composition, and the pressure of the compositionis higher than the pressure of the target reservoir 206 (i.e.,P1>P2>P3). The highest pressure of the source reservoir 202 causes thewater to flow from the source reservoir 202 towards a region of lowerpressure, that is, the water collection zone 222, the chemical injectiontubing 702, and through the static mixer 706 to the target reservoir 206with the lowest pressure. Similarly, the pressure of the LP compositioncauses it to flow towards a region of lower pressure, that is, throughthe static mixer 706 to the target reservoir 206 with the lowestpressure. As the pressure of the source reservoir 202 is higher than thepressure of the LP composition, the LP composition will not flow towardsthe source reservoir 202.

Like in FIG. 9, the pressure differences can drive the water, the LPcomposition, or both to their destinations in some of the otherembodiments as well. Moreover, a pump (e.g., the pump 216, the ESP 306,502 and the PCP 402, 604), a valve (e.g., the one way valves 610, 612),pressure differences, or any combination thereof can be used to drivethe water, the LP composition, or both to their destinations. Forexample, in FIG. 7, (a) the highest pressure of the source reservoir 202causes the water to flow from the source reservoir 202 towards a regionof lower pressure such as the water collection zone 222, (b) thecontents of the water collection zone 222 are drawn into the ESP 502 bythe operation of the ESP 502, and (c) the contents in the ESP 502 travelthrough the water injection tubing 506 and into the injection zone 226by the operation of the ESP 502.

As discussed above, the inverted polymer solutions described herein canbe used oil and gas operations, such as EOR operations. For example, theinverted polymer solutions described above can be used in polymerflooding operations. In some cases, the inverted polymer solutionfurther includes one or more additional agents to facilitate hydrocarbonrecovery. For example, the inverted polymer solution can further includea surfactant, an alkalinity agent, a co-solvent, a chelating agent, orany combination thereof. As such, the inverted polymer solution can beused in polymer (P), alkaline-polymer (AP), surfactant-polymer (SP),and/or in alkaline-surfactant-polymer (ASP)-type EOR operations. Whenpresent, these additional components can be incorporated to the aqueousfluid used to invert the LP composition prior to inversion of the LPcomposition. Alternatively, these additional components can beincorporated to the inverted polymer solutions following inversion ofthe LP composition.

For chemical enhanced oil recovery (CEOR) operations, the LP compositioncan be dispersed into an aqueous stream in a sufficient amount for aninjection stream with a target hydrated polymer concentration andparticle size. The target concentration varies according to the type ofpolymer employed, as well as the characteristics of the reservoir, e.g.,petrophysical rock properties, reservoir fluid properties, reservoirconditions such as temperature, permeability, water compositions,mineralogy and/or reservoir location, etc. In some cases, the invertedpolymer solutions described herein are suitable for use in reservoirswith a permeability of from 10 millidarcy to 40,000 millidarcy.

The hydrated polymer molecules in the inverted polymer solution can havea particle size (radius of gyration) ranging from 0.01 to 10 μm in oneembodiment. One reservoir characteristic is the median pore throats,which correspond to the permeability of the reservoirs. Depending on thereservoir, the median pore throats in reservoirs may range from 0.01 μmto several hundred micrometers. Since the size of hydrated polymers inwater range from 0.01 micrometer to several micrometers depending on thespecies, molecules, and reservoir conditions, in one embodiment,appropriate polymers are selected for LP composition to afford aninverted polymer solution where the particle size of the hydratedpolymer is <10% of the median pore throat parameters. This can allow thehydrated polymer particles to flow through the porous medium in anuninhibited manner. In another embodiment, the hydrated polymerparticles have an average particle size ranging from 2 to 8% of themedian pore throat size.

Surfactants can be included to lower the interfacial tension between theoil and water phase to less than about 10-2 dyne/cm (for example) andthereby recover additional oil by mobilizing and solubilizing oiltrapped by capillary forces. Examples of surfactants that can beutilized include, but are not limited to, anionic surfactants, cationicsurfactants, amphoteric surfactants, non-ionic surfactants, or acombination thereof. Anionic surfactants can include sulfates,sulfonates, phosphates, or carboxylates. Such anionic surfactants areknown and described in the art in, for example, U.S. Pat. No. 7,770,641,incorporated herein by reference in its entirety. Examples of specificanionic surfactants include internal olefin sulfonates, isomerizedolefin sulfonates, alkyl aryl sulfonates, medium alcohol (C10 to C17)alkoxy sulfates, alcohol ether [alkoxy] carboxylates, and alcohol ether[alkoxy] sulfates. Example cationic surfactants include primary,secondary, or tertiary amines, or quaternary ammonium cations. Exampleamphoteric surfactants include cationic surfactants that are linked to aterminal sulfonate or carboxylate group. Example non-ionic surfactantsinclude alcohol alkoxylates such as alkylaryl alkoxy alcohols or alkylalkoxy alcohols. Other non-ionic surfactants can include alkylalkoxylated esters and alkyl polyglycosides. In some embodiments,multiple non-ionic surfactants such as non-ionic alcohols or non-ionicesters are combined. As a skilled artisan may appreciate, thesurfactant(s) selection may vary depending upon such factors assalinity, temperature, and clay content in the reservoir.

Suitable alkalinity agents include basic, ionic salts of alkali metalsor alkaline earth metals. Alkalinity agents can be capable of reactingwith an unrefined petroleum acid (e.g. the acid or its precursor incrude oil (reactive oil)) to form soap (a surfactant which is a salt ofa fatty acid) in situ. These in situ generated soaps can serve as asource of surfactants causing a reduction of the interfacial tension ofthe oil in water emulsion, thereby reducing the viscosity of theemulsion. Examples of alkali agents include alkali metal hydroxides,carbonates, or bicarbonates, including, but not limited to, sodiumcarbonate, sodium bicarbonate, sodium hydroxide, potassium hydroxide,sodium silicate, tetrasodium EDTA, sodium metaborate, sodium citrate,and sodium tetraborate. In some cases, the alkalinity agent can bepresent in the inverted polymer solution in an amount of from 0.3 to 5.0weight percent of the solution, such as 0.5 to 3 weight percent.

The inverted polymer solution can optionally include a co-solvent. A“co-solvent” refers to a compound having the ability to increase thesolubility of a solute in the presence of an unrefined petroleum acid.In embodiments, the co-solvents provided herein have a hydrophobicportion (alkyl or aryl chain), a hydrophilic portion (e.g. an alcohol)and optionally an alkoxy portion. Co-solvents as provided herein includealcohols (e.g. C₁-C₆ alcohols, C₁-C₆ diols), alkoxy alcohols (e.g. C₁-C₆alkoxy alcohols, C₁-C₆ alkoxy diols, and phenyl alkoxy alcohols), glycolether, glycol and glycerol. The term “alcohol” is used according to itsordinary meaning and refers to an organic compound containing an —OHgroups attached to a carbon atom. The term “diol” is used according toits ordinary meaning and refers to an organic compound containing two—OH groups attached to two different carbon atoms. The term “alkoxyalcohol” is used according to its ordinary meaning and refers to anorganic compound containing an alkoxy linker attached to a —OH group.

The inverted polymer solution can optionally include a chelant orchelating agent. Chelants may be used to complex with the alkali metaland soften brines. If desired, the salinity of the inverted polymersolution may be optimized for a particular subterranean reservoir byadjusting a number of chelating ligands in the chelating agent, such asalkoxylate groups if the chelant is EDTA (“ethylenediaminetetraaceticacid”). EDTA is just one example of a suitable chelant, another exampleof a chelant is MGDA (“methylglycinediacetic acid”).

If desired, other additives can also be included in inverted polymersolutions described herein, such as biocides, oxygen scavengers, andcorrosion inhibitors.

Methods of Use

The inverted polymer solutions described herein can be used in a varietyof oil and gas operations, including an EOR operation (e.g., an improvedoil recovery (IOR) operation, a polymer flooding operation, an APflooding operation, a SP flooding operation, an ASP flooding operation,a conformance control operation, or any combination thereof). Moreover,the inverted polymer solutions described herein can be used in a varietyof oil and gas operations, including a hydraulic fracturing operation,as a drag reducer that reduces friction during transportation of a fluidin a pipeline, or any combination thereof. Transportation of a fluid ina pipeline can refer to any movement of a fluid through a conduit orpipe. As such, transportation of a fluid in a pipeline includes, forexample, the pipeline transport of fluids as well as passage of fluidsthrough pipes such as wellbores during the course of an oil recoveryoperation. The inverted polymer solutions can even be used in watertreatment operations associated with oil and gas operations.

In one embodiment, the inverted polymer solution can be used as aninjection fluid. In another embodiment, the inverted polymer solutioncan be included in an injection fluid. In another embodiment, theinverted polymer solution can be used as a hydraulic fracturing fluid.In another embodiment, the inverted polymer solution can be included ina hydraulic fracturing fluid. In another embodiment, the invertedpolymer solution can be used as a drag reducer that reduces frictionduring transportation of a fluid in a pipeline. In another embodiment,the inverted polymer solution can be included in a drag reducer thatreduces friction during transportation of a fluid in a pipeline. Inshort, in certain embodiments, the inverted polymer solutions describedherein can be used in hydrocarbon recovery.

Methods of hydrocarbon recovery can comprise providing a subsurfacereservoir containing hydrocarbons therewithin; providing a wellbore influid communication with the subsurface reservoir; preparing an invertedpolymer solution using the methods described above; and injecting theinverted polymer solution through the wellbore into the subsurfacereservoir. For example, the subsurface reservoir can be a subseareservoir and/or the subsurface reservoir can have a permeability offrom 10 millidarcy to 40,000 millidarcy.

The wellbore in the second step can be an injection wellbore associatedwith an injection well, and the method can further comprise providing aproduction well spaced-apart from the injection well a predetermineddistance and having a production wellbore in fluid communication withthe subsurface reservoir. In these embodiments, injection of theinverted polymer solution can increase the flow of hydrocarbons to theproduction wellbore.

In some embodiments, methods of hydrocarbon recovery can further includea recycling step. For example, in some embodiments, methods ofhydrocarbon recovery can further comprise producing production fluidfrom the production well, the production fluid including at least aportion of the injected inverted polymer solution; and using theproduction fluid to invert additional LP composition, for example, tofor form a second inverted polymer solution. The second inverted polymersolution can be injected into at least one wellbore (e.g., an injectionwell, the same wellbore discussed in the second step or a differentwellbore, etc.). Thus, in some embodiments, the inverted polymersolution is included in an injection fluid.

The wellbore in the second step can be a wellbore for hydraulicfracturing that is in fluid communication with the subsurface reservoir.Thus, in one embodiment, the inverted polymer solution injected in thefourth step functions as a drag reducer that reduces friction duringinjection in the fourth step. By doing so, the inverted polymer solutionis used as a drag reducer that reduces friction during transportation ofa fluid (e.g., the hydraulic fracturing fluid) in a pipeline (e.g., thewellbore or components thereof). In another embodiment, the invertedpolymer solution is included in a hydraulic fracturing fluid.

By way of non-limiting illustration, examples of certain embodiments ofthe present disclosure are given below.

EXAMPLES Methods and Materials

A synthetic brine was used as base brine. The synthetic brine includedthe following: Na⁺, Ca²⁺, Mg²⁺, Cl⁻, and a TDS of about 15,000 ppm.Since the neat liquid polymer (LP) was provided as an oil-continuouspolymer dispersion with an activity of 50%, the LP polymer was invertedand diluted to target concentration of 2000 ppm in the synthetic brineby mixing at 500 rpm using an overhead mixer. In the laboratory, 50%neat liquid polymer was inverted to 1% LP solution in the syntheticbrine using the overhead mixer at 500 rpm for 2 hours. Then, the 1%inverted LP solution was diluted to the targeted 0.2% LP solution in thesynthetic brine using the overhead mixer at 500 rpm for 2 hours to 24hours. 50% neat liquid polymer was also directly inverted to the targetconcentration of 0.2% LP polymer in the synthetic brine using theoverhead mixer for 3 hours to 24 hours.

Since the neat liquid polymer (LP) was provided as an oil-continuouspolymer dispersion with an activity of 50%, the LP polymer was invertedand diluted to target concentration of 2000 ppm in synthetic brine bymixing at 500 rpm using an overhead mixer. In the laboratory, 50% neatliquid polymer was inverted to 1% LP solution in synthetic brine usingthe overhead mixer at 500 rpm for 2 hours. Then, the 1% inverted LPsolution was diluted to the targeted 0.2% LP solution in synthetic brineusing the overhead mixer at 500 rpm for 2 hours to 24 hours. 50% neatliquid polymer was also directly inverted to the target concentration of0.2% LP polymer in synthetic brine using the overhead mixer for 3 hoursto 24 hours.

The filter ratio (FR) of the inverted polymer solutions was determinedusing the standard procedure described, for example, in Koh, H.Experimental Investigation of the Effect of Polymers on Residual OilSaturation. Ph.D. Dissertation, University of Texas at Austin, 2015;Levitt, D. The Optimal Use of Enhanced Oil Recovery Polymers UnderHostile Conditions. Ph.D. Dissertation, University of Texas at Austin,2009; and Magbagbeola, O. A. Quantification of the Viscoelastic Behaviorof High Molecular Weight Polymers used for Chemical Enhanced OilRecovery. M.S. Thesis, University of Texas at Austin, 2008, each ofwhich is hereby incorporated by reference in its entirety. Briefly, a300 ml solution of 2000 ppm inverted LP solution in synthetic brine wasfiltered through a 5.0 μm and 1.2 μm ISOPORE™ polycarbonate filter witha diameter of 47 mm at 15 psi (plus or minus 10% of 15 psi) pressure andambient temperature (25° C.). As expressed in the formula below, the FRwas calculated as the ratio of the time for 180 to 200 ml of the polymersolution to filter divided by the time for 60 to 80 ml of the polymersolution to filter.

${FR} = \frac{{\;^{t}200\mspace{14mu}{ml}} - {{\,^{t}180}\mspace{14mu}{ml}}}{{\;^{t}80\mspace{14mu}{ml}} - {{\,^{t}60}\mspace{14mu}{ml}}}$For the composition to qualify for further testing, the composition wasrequired to exhibit a FR of less than or equal to 1.2 through bothfilters. As the 1.2 FR was a strict laboratory requirement for polymerqualification, clean, laboratory-grade filtered water was used whennecessary.

Steady-state shear viscosities were measured in the range of 0.1 s−1 to1000 s−1 at 25° C., and 31° C. using double-wall couette geometry with aTA Instruments ARES-G2 rheometer.

Polymer injectivity tests were performed separately using 2000 ppm LP ina 2000 mD Bentheimer sandstone at 31° C. The flow rate was set at 0.5mL/min, corresponding to ˜6 ft/day. The differential pressure dropbetween inlet and outlet was measured using Rosemount differentialpressure transducers.

Oil recovery experiments were performed using 2000 ppm LP using anapproximately 5000 mD unconsolidated-sand pack at 31° C. The flow ratewas set at 0.5 mL/min, corresponding to ˜4 ft/day. The differentialpressure drop between inlet and outlet was measured using Rosemountdifferential transducers. A viscous crude oil (80 cP at 31° C.) wasselected in this experiment.

Results and Discussion

FR test: FIG. 11 shows a plot of the FR test performed for an invertedpolymer solution using a 1.2 micron filter with a diameter of 47 mm at15 psi pressure and 25° C. temperature. As shown in FIG. 11 and Table 2,the inverted LP solution (2000 ppm polymer) passes through 1.2 micronfilter with a FR of less than or equal to 1.5. More specifically, FIG.11 illustrates a FR of 1.2 or less. Even more specifically, FIG. 11illustrates a FR of 1.13. This result indicates the improvedfilterability of the inverted polymer solution.

Viscosity measurement: FIG. 12 shows a viscosity plot for a wide rangeof shear rates for an inverted polymer solution (2000 ppm polymer insynthetic brine, measured at 31° C.). The viscosity of the invertedpolymer solution illustrates a typical shear-thinning behavior in thewide range of shear rate. The viscosity is measured as 24 cP at 10 s−1and 31° C.

Injectivity Test: The inverted polymer solution was injected intooutcrop Bentheimer sandstones. The purpose of the polymer injection wasto evaluate the injectivity of the inverted polymer solution in theporous medium. Around 30 PV of 2000 ppm LP polymer in synthetic brinewas injected into Bentheimer sandstone at flow rate of 0.5 ml/mincorresponding to 6 ft./day at the temperature of 31° C. As shown in FIG.10, the pressure drop for the inverted polymer solution reachessteady-state after 2 pore volume (PV) which indicates no plugging. Thecorresponding relative permeability history is also plotted in FIG. 10.The relative permeability of the inverted polymer solution after 28 PVwas ˜1 which confirms core plugging.

Oil Recovery experiment: The ability of the inverted polymer solution todisplace oil and improve recovery was tested in Bentheimer sandstone inthe presence of crude oil. A viscous crude oil (80 cP at 31° C.) waschosen for the test. The inverted polymer solution was injected at theend of water flooding in separate core flooding experiments. The oilrecovery and pressure drop is plotted in FIG. 14. As seen in Figures,oil recovery improves as the inverted LP solution is injected whilepressure drop for LP injection shows steady-state and low at the end ofthe experiment. The steady-state low pressure drop for LP solution atthe end of the experiment indicates improved behavior as the LP solutiondo not plug the core during oil recovery

TABLE 2 Summary of properties of inverted LP composition. 5 μm filter1.2 μm filter Polymer (15 psi, 25° C.) ( 15 psi, 25 C.) ViscosityConcen- Time to Time to (cP) @ Poly- tration 200 g 200 g 31° C. mer(ppm) F.R (min) F.R (min) 10 s⁻¹ LP 2000 1.00 5.0 1.13 27 22 2000 1.014.4 1.19 25 21 2000 1.04 5.7 1.18 24 25

Validation of filtration test and viscosity measurements usingpilot-scale LP samples: Additional filtration ratio test and viscositymeasurements were performed using larger-scale produced samples. Theseinclude pilot-scale and commercial field-scale samples compared withprevious lab-scale manufactured samples. The results of filtration ratioand viscosity measurement have been summarized in Table 3.

The viscosity yield as a function of concentration of polymer used wasmeasured at 31° C. FIG. 15 shows the viscosity yield curve as a functionof concentration. Mother solution of 10,000 ppm concentrate was preparedfrom 52% active neat polymer. From this mother solution, appropriatedilutions were made and viscosities measured between 0.1 sec⁻¹ and 1000sec⁻¹. The viscosity values in FIG. 15 correspond to a shear rate of 10sec⁻¹. At a concentration of 2000 ppm inverted polymer solution, theviscosity is about 23 cP and the viscosity yield of 10,000 ppm invertedpolymer solution is approximately 900 cP. FIG. 16 shows the polymerviscosity as a function of shear rate. As shown in FIG. 16 shearthinning behavior of polymer solutions was observed. As the polymerconcentrations increased, the shear thinning behavior changed from lessshear thinning to more shear thinning.

TABLE 3 Summary of filtration and viscosity data using pilot-scalesamples. Viscosity (cP) @10 s⁻¹ Filtration Ration Test @ 15 psi, 25 C.Neat 2k ppm F.R. time to F.R. time to Sample Activity (25 C.) (31 C.) (5μm) 200 g (m) (1.2 um) 200 g (m) S-1 52.4% 179 25 1.04 5.7 1.18 24 22 15 1.13 27 21 1.01 4.4 1.19 25 M-1 52.1% 152 26 1.05 6.2 1.32 28.4 1.036.0 1.22 25.2 1.43 30.0 M-2 51.8% 128 25 1.04 6.1 1.44 30.8 M-3 50.3%104 24 1.04 6.3 1.24 29.4 1.31 27.4 16 1.34 13.2 20 1.50 21.0 M-5 50.5%101 21 1.04 5.0 1.24 24.0 1.39 26.2 19 1.22 14.4 19 1.30 16.5 M-6 51.2%107 21 1.03 4.8 1.31 26.0 1.37 27.8 18 1.21 16.0 PL#5 50.0% 241 22 1.1316.0 PL#6 50.0% 252 20 1.27 16.0 TL#2 50.0% 599 24 1.24 20.5 Mean 207 211.04 5.51 1.28 23.1 Std. Dev 148 3 0.02 0.66 0.10 5.5

2000 ppm inverted polymer solutions were prepared using differentpilot-scale batches of LP solutions (M1 through M5) and filtration testswere performed as described above. FIGS. 17A and 17B show the results offiltration ratio tests performed with different pilot-scale batches ofLP solutions using a 5 micron filter (FIG. 17A) and 1.2 micron filter(FIG. 17B) at 15 psi. As shown in FIGS. 17A and 17B, the LP solutionsproduce a FR of 1.04+/−0.02 for a 5 micron filter and 1.28+/−0.1 for a1.2 micron filter.

FIG. 18 shows a long-term injectivity test of single phase invertedpolymer solution in a core. The core included a pressure tap two inchesfrom the face, providing a pressure differential across the injectionface of the core. As shown in FIG. 18, the steady-state pressure dropshowed no significant signal consistent with plugging of the sandstonecore. Analysis of the pressure drop during the post-water flood alsoshowed no plugging.

To verify the long-term injectivity performance of the inverted LPsolutions, the relative permeability of the single phase polymer floodwas normalized using methods known in the art (see SPE 179657, SPE IORsymposium at Tulsa 2016, which is incorporated herein by reference inits entirety). FIG. 19A shows the relative plugging when the results arenormalized for each section with total pore volumes injected for aconventional emulsion polymer. These results indicate that the pluggingrate is faster near the injection face compared to subsequent sectionsof the core. In contrast, as shown in FIG. 19B, the inverted LPsolutions do not exhibit any significant signs of plugging.

FIG. 20 shows the permeability Reduction Factor (Rk) and Normalized SkinFactor, s/ln(r_(s)/r_(w)) vs. filtration ratio at 1.2 μm (FR 1.2). Asshown in FIG. 20, Rk and skin factor both increase when FR is greaterthan 1.5. These results suggest that injection of a polymer solutionwith a FR greater than 1.5 plugs the core, while injection of a polymersolution with a FR of 1.5 or less causes no plugs to the core.

Polymer loop yard tests: With polymer mixing and performance inlaboratory conditions validated, the next step was to evaluate themixing efficiency of the neat solution in brine to a final 2000 ppmpolymer concentration in larger scale yard tests. The goal of the yardtests was to demonstrate that acceptable viscosity yield and filtrationratio could be achieved using single step configuration mixers andmulti-step configuration mixers (with and without dynamic mixers) asdescribed in FIGS. 1 and 2.

Experimental results using a single step mixer configuration aresummarized in Table 3 and experimental results using a multi-step mixerconfiguration are summarized in Table 4. Each experiment was performedusing different size static mixer elements and different configurationsincluding dynamic mixer, different flow rate and different ratio of neatpolymer and brine. The samples were collected after each run, andfiltration tests and viscosity measurements were performed to verify thehydration of the LP including inversion and dilution through thedesigned mixing system.

TABLE 4 Summary of polymer loop yard test - example of single stepmixing. Pressure Viscosity Filtration across Mixer Flow (cP, 31 C.) FRTime the Mixing 1st stage 2nd stage rate Velocity Dynamic 7.3 10 (1.2(min, mixer Run # Scheme (Inversion) (Dilution) gpm (m/s) mixer s-1 s-1μm) 200 g) (psi) S-1 Single 1″ϕ:15 elements 30 3.7 Y 21.7 18.8 1 120 120step S-2 Single 1″ϕ:15 elements 30 3.7 N 21.2 19.5 1.14 83 125 step S-3Single 2″ϕ:15 elements 95 3 Y 26.7 23.3 1 120 120 step S-4 Single 2″ϕ:15elements 95-100 3.1 N 26.7 23.6 1.07 100 180 step

TABLE 5 Summary of polymer loop yard test - example of multistep mixing.Pressure Viscosity Filtration across Mixer Flow (cP, 31 C.) FR Time theMixing 1st stage 2nd stage rate Velocity Dynamic 7.3 10 (1.2 (min, mixerRun # Scheme (Inversion) (Dilution) gpm (m/s) mixer s-1 s-1 μm) 200 g)(psi) M-1 Two step 1″ϕ:15 2″ϕ:15  125- 3.4/3.9 N 26.2 23 1.3 95 140elements elements 130 M-2 Two step 1″ϕ:15 2″ϕ:15 125 3.4/3.9 Y 23 20.11.13 99 140 elements elements M-3 Two step 1″ϕ:15 2″ϕ:15 100 2.5/3.1 Y23 20 1.2 85 100 elements elements

As shown in FIG. 21, viscosity yields were measured above 20 cP in bothmulti-step (two) mixing configuration and single step mixingconfiguration with and without the dynamic mixer. This shows that the LPproperly hydrates through the static mixers in both a single-step or inmulti-step configuration. FIGS. 22A and 22B show the viscosity yield asa function of pressure drop across the static mixers (FIG. 22A) andfiltration ratio as a function of pressure drop across the static mixers(FIG. 22B). To hydrate the LP and provide a suitable viscosity yield andfilterability, a FR of 1.5 or less at 1.2 micron should be used.

Overall, the polymer loop yard tests demonstrate that successfulviscosity yields can be achieved with a suitable filtration ratio usingeither a single step or multi-step mixing process. Furthermore,injectivity experiments through surrogate rock showed no appreciableplugging behavior.

The compositions and methods of the appended claims are not limited inscope by the specific compositions and methods described herein, whichare intended as illustrations of a few aspects of the claims. Anycompositions and methods that are functionally equivalent are intendedto fall within the scope of the claims. Various modifications of thecompositions and methods in addition to those shown and described hereinare intended to fall within the scope of the appended claims. Further,while only certain representative compositions and method stepsdisclosed herein are specifically described, other combinations of thecompositions and method steps also are intended to fall within the scopeof the appended claims, even if not specifically recited. Thus, acombination of steps, elements, components, or constituents may beexplicitly mentioned herein or less, however, other combinations ofsteps, elements, components, and constituents are included, even thoughnot explicitly stated.

The term “comprising” and variations thereof as used herein is usedsynonymously with the term “including” and variations thereof and areopen, non-limiting terms. Although the terms “comprising” and“including” have been used herein to describe various embodiments, theterms “consisting essentially of” and “consisting of” can be used inplace of “comprising” and “including” to provide for more specificembodiments of the invention and are also disclosed. Other than wherenoted, all numbers expressing geometries, dimensions, and so forth usedin the specification and claims are to be understood at the very least,and not as an attempt to limit the application of the doctrine ofequivalents to the scope of the claims, to be construed in light of thenumber of significant digits and ordinary rounding approaches.

It is understood that when combinations, subsets, groups, etc. ofelements are disclosed (e.g., combinations of components in acomposition, or combinations of steps in a method), that while specificreference of each of the various individual and collective combinationsand permutations of these elements may not be explicitly disclosed, eachis specifically contemplated and described herein. By way of example, ifa composition is described herein as including a component of type A, acomponent of type B, a component of type C, or any combination thereof,it is understood that this phrase describes all of the variousindividual and collective combinations and permutations of thesecomponents. For example, in some embodiments, the composition describedby this phrase could include only a component of type A. In someembodiments, the composition described by this phrase could include onlya component of type B. In some embodiments, the composition described bythis phrase could include only a component of type C. In someembodiments, the composition described by this phrase could include acomponent of type A and a component of type B. In some embodiments, thecomposition described by this phrase could include a component of type Aand a component of type C. In some embodiments, the compositiondescribed by this phrase could include a component of type B and acomponent of type C. In some embodiments, the composition described bythis phrase could include a component of type A, a component of type B,and a component of type C. In some embodiments, the compositiondescribed by this phrase could include two or more components of type A(e.g., A1 and A2). In some embodiments, the composition described bythis phrase could include two or more components of type B (e.g., B1 andB2). In some embodiments, the composition described by this phrase couldinclude two or more components of type C (e.g., C1 and C2). In someembodiments, the composition described by this phrase could include twoor more of a first component (e.g., two or more components of type A (A1and A2)), optionally one or more of a second component (e.g., optionallyone or more components of type B), and optionally one or more of a thirdcomponent (e.g., optionally one or more components of type C). In someembodiments, the composition described by this phrase could include twoor more of a first component (e.g., two or more components of type B (B1and B2)), optionally one or more of a second component (e.g., optionallyone or more components of type A), and optionally one or more of a thirdcomponent (e.g., optionally one or more components of type C). In someembodiments, the composition described by this phrase could include twoor more of a first component (e.g., two or more components of type C (C1and C2)), optionally one or more of a second component (e.g., optionallyone or more components of type A), and optionally one or more of a thirdcomponent (e.g., optionally one or more components of type B).

This application relates to the subject matter of U.S. ProvisionalApplication No. 62/264,772, filed Dec. 8, 2015; U.S. ProvisionalApplication No. 62/264,700, filed Dec. 8, 2015; U.S. ProvisionalApplication No. 62/264,701, filed Dec. 8, 2015; and U.S. ProvisionalApplication No. 62/264,703, filed Dec. 8, 2015; each of which is herebyincorporated herein by reference in its entirety.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meanings as commonly understood by one of skill in the artto which the disclosed invention belongs. Publications cited herein andthe materials for which they are cited are specifically incorporated byreference.

What is claimed is:
 1. A method for preparing an inverted polymersolution comprising providing a liquid polymer (LP) compositioncomprising: one or more hydrophobic liquids having a boiling point of atleast 100° C.; at least 39% by weight of one or more synthetic(co)polymers; one or more emulsifier surfactants; and one or moreinverting surfactants; inverting the LP composition in an aqueous fluidto provide an inverted polymer solution having a concentration ofsynthetic (co)polymer of from 50 to 15,000 ppm; wherein the invertedpolymer solution has a filter ratio of 1.5 or less at 15 psi using a 1.2μm filter; and wherein the inverted polymer solution is used in anenhanced oil recovery (EOR) operation.
 2. The method of claim 1, whereinthe inverted polymer solution has a filter ratio of from 1.1 to 1.3 at15 psi using the 1.2 μm filter.
 3. The method of claim 1, wherein theinversion of the LP composition forms the inverted polymer solution in30 minutes or less.
 4. The method of claim 1, wherein the inversion ofthe LP composition comprises a continuous process.
 5. The method ofclaim 1, wherein the inversion of the LP composition comprises a singlestep, and wherein the single step comprises diluting the LP compositionin the aqueous fluid in an in-line mixer having a mixer inlet and amixer outlet to provide the inverted polymer solution.
 6. The method ofclaim 5, wherein the difference in pressure between the mixer inlet andthe mixer outlet is from 15 psi to 400 psi.
 7. The method of claim 5,wherein the in-line mixer is positioned on the surface, subsurface,subsea, or downhole.
 8. The method of claim 1, wherein the inversion ofthe LP composition comprises multiple steps.
 9. The method of claim 8,wherein the inversion of the LP composition comprises: as a first step,inverting the LP composition in the aqueous fluid in a first in-linemixer having a first mixer inlet and a first mixer outlet to provide aconcentrated polymer composition having a concentration of synthetic(co)polymer of up to 15,000 ppm; and as a second step, diluting theconcentrated polymer composition in the aqueous fluid in a secondin-line mixer having a second mixer inlet and a second mixer outlet toprovide the inverted polymer solution.
 10. The method of claim 9,wherein the difference in pressure between the first mixer inlet and thefirst mixer outlet is from 15 psi to 400 psi.
 11. The method of claim 9,wherein the first in-line mixer is positioned on the surface,subsurface, subsea, or downhole.
 12. The method of claim 9, wherein thedifference in pressure between the second mixer inlet and the secondmixer outlet is from 15 psi to 400 psi.
 13. The method of claim 1,wherein the aqueous fluid comprises soft brine or hard brine.
 14. Themethod of claim 1, wherein the aqueous fluid comprises producedreservoir brine, reservoir brine, sea water, fresh water, producedwater, water, saltwater, brine, synthetic brine, synthetic seawaterbrine, or any combination thereof.
 15. The method of claim 1, whereinthe aqueous fluid further comprises a surfactant, an alkalinity agent, aco-solvent, a chelating agent, or any combination thereof.
 16. Themethod of claim 1, wherein the inversion of the LP composition comprisesparallel single steps, parallel multiple steps, or any combinationthereof.
 17. The method of claim 16, wherein the parallel single steps,parallel multiple steps, or any combination thereof include using atleast one in-line mixer for diluting the LP composition in the aqueousfluid, the in-line mixer having a mixer inlet and a mixer outlet toprovide the inverted polymer solution.
 18. The method of claim 17,wherein the difference in pressure between the mixer inlet and the mixeroutlet is from 15 psi to 400 psi.
 19. The method of claim 17, whereinthe in-line mixer is positioned on the surface, subsurface, subsea, ordownhole.
 20. The method of claim 1, wherein the one or more synthetic(co)polymers comprise one or more acrylamide (co)polymers.
 21. Themethod of claim 1, wherein the inverted polymer solution is used as aninjection fluid.
 22. The method of claim 1, wherein the inverted polymersolution is included in an injection fluid.
 23. The method of claim 1,wherein the EOR operation includes a polymer flooding operation, an APflooding operation, a SP flooding operation, an ASP flooding operation,a conformance control operation, or any combination thereof.
 24. Amethod for preparing an inverted polymer solution comprising providing aliquid polymer (LP) composition in the form of an inverse emulsioncomprising: one or more hydrophobic liquids having a boiling point of atleast 100° C.; up to 35% by weight of one or more synthetic(co)polymers; one or more emulsifier surfactants; and one or moreinverting surfactants; inverting the LP composition in an aqueous fluidto provide an inverted polymer solution having a concentration ofsynthetic (co)polymer of from 50 to 15,000 ppm; wherein the invertedpolymer solution has a filter ratio of 1.5 or less at 15 psi using a 1.2μm filter; and wherein the inverted polymer solution is used in anenhanced oil recovery (EOR) operation.
 25. A method for hydrocarbonrecovery, comprising: (a) providing a subsurface reservoir containinghydrocarbons there within; (b) providing a wellbore in fluidcommunication with the subsurface reservoir; (c) providing a liquidpolymer (LP) composition comprising: one or more hydrophobic liquidshaving a boiling point of at least 100° C.; at least 39% by weight ofone or more synthetic (co)polymers; one or more emulsifier surfactants;and one or more inverting surfactants; (d) inverting the LP compositionin an aqueous fluid to provide an inverted polymer solution having aconcentration of synthetic (co)polymer of from 50 to 15,000 ppm; whereinthe inverted polymer solution has a filter ratio of 1.5 or less at 15psi using a 1.2 μm filter; and (e) injecting the inverted polymersolution through the wellbore into the subsurface reservoir.